Epic Fajitas Vegan Portobello Mushroom Burger

Large portobello mushroom caps are marinated in a fajita spice mix and layered among guacamole, salsa, nacho cheese sauce, and spicy fajitas veggies. This vegan portobello mushroom burger is piquant and scrumptious at the same time. 

This mushroom burger recipe was inspired by our vegan portobello mushroom fajitas. It is rich, colorful, and full of flavors. If you also love Tex-Mex food try our classic vegan bean chili, our quinoa sweet potato chili, our vegan taco soup, or our Mexican vegan rice casserole recipes.

What can you expect from this recipe?

If you’ve never eaten it before, then you are in for a treat. In this burger recipe, you marinate and grill large portobello mushroom caps in whole and use them instead of regular burger patties.

Obviously, it is something different from a classic beef burger. If you looking for a beefy texture, try our vegan burger with TVP. I would say this recipe is closer to grilled chicken in terms of texture.

You can add these grilled mushroom caps to any burger recipe. May it be with a hamburger bun full of shredded lettuce, sliced tomato, and red onion rings, or try this spicy fajita-inspired vegan burger recipe? I can list several reasons.

This grilled portobello mushroom burger…

• is piquant and creamy at the same time.
• is full of rich and colorful ingredients.
• has a charred flavor and a meaty texture.
• is healthier than beef burgers.
• is easy to make and incredibly tasty.

In one word, it is EPIC. Need I say more? Now, let’s see how to make one!

Ingredients

To build this vegan portobello mushroom burger, here is what you need:

• Large portobello mushroom caps -> marinated in fajitas spice mix, garlic, lime, sweet smoked paprika powder, salt, black pepper, and olive oil
• Lettuce leaves
• Fajita veggies -> we have a recipe for an easy sheet pan version where you can make a large batch in one go
• Guacamole
• Salsa
• Vegan nacho cheese sauce -> this recipe is a nut-free version made of mostly root veggies
• Hamburger bun

If you don’t have a fajitas seasoning in your pantry, don’t worry you can easily make your own using the below spices:

• hot chili powder,
• sweet smoked paprika,
• cumin,
• garlic powder, and
• oregano.

🛒 You can find detailed measurements for all ingredients in the printable version of the recipe card at the bottom of this post.

Instructions

Marinating

1. Take a small-sized bowl
2. Add olive oil, salt, black pepper, minced garlic cloves, freshly squeezed lime juice, fajitas spice mix, and smoked sweet paprika powder.
3. Stir until they are thoroughly combined. See how this marinade looks in the below picture.

4. Peel portobello mushroom caps with a sharp knife and take out the stems.
5. Take a glass bowl (the one in the photo is also our meal prep bowl) and place the mushroom caps in it. If you make multiple servings, choose a bowl that would fit them in one layer.
6. Pour the marinade on top of them. Use a silicone brush to spread the marinade. Toss and turn a couple of times, to make sure they are covered everywhere.
7. Repeat this step once more after an hour or in the morning if you marinate them overnight to make sure mushrooms are not getting dry. In the end, it will look like the ones in the below photo.

How to cook portobello mushroom burgers? We will show you 3 ways to make them delicious. You either bake them, grill them or pan-fry them.

Top tips for marinating mushrooms

• How long? – Mushrooms have a spongy texture. Therefore, the longer they soak in the marinade, the more intense the flavor will be as they absorb more. We recommend overnight soaking, but 2 hours should be the bare minimum to get them seasoned properly.
• How much? – You don’t need to make a lot of marinades as you don’t need to immerse the mushroom caps in it. We do flip them or brush them a couple of times.
• Hot or sweet? – In case you prepare the burger for kids or for people who don’t like spicy food, you can skip the hot chili powder and add more sweet smoked paprika powder.
• Powder vs fresh ingredients? – We like using fresh ingredients if we have them, but you can use onion powder or garlic powder instead.

Pan-frying

The easiest way is if you have a grill pan and you cook them on a stovetop.

1. Preheat the grill pan over medium heat.
2. Once it is sizzling hot, place the marinated mushroom caps on it. No need to add extra oil since the marinade already contains enough.
3. Gently push the mushrooms down for a few seconds on each side with a spatula to allow the greater surface of the mushrooms to be grilled.
4. Brush each side with the leftover marinade once.
5. Cover the grill pan to allow hot air to circulate through the pan (just as it would in a real gas grill) and cook both sides for approx. 5 minutes each. That is all! You can see how they look when they are ready in the below picture. Now, you are ready to assemble your vegan portobello mushroom burger.

Baking

You can use a glass oven-safe dish or a grill pan (provided that the handle is not made of plastic). Preheat the oven to 400 Fahrenheit (200 degrees Celsius) and grill them under the broiler for 10 minutes, turning them at halftime.

Grilling without burning them

Our little trick to grilling mushrooms is to use aluminum foil drip pans. Preheat your gas grill to 400 Fahrenheit (200 degrees Celsius) and grill the marinated portobello mushroom caps for 10 minutes, turning them at halftime.

How to build this burger?

The best part of the whole recipe is building your yummy portobello burger. I know that the more layers you add, the harder it is to eat. However, I really-really recommend all these layers for you to try. They are absolutely amazing and delicious together!

1. I started off with a toasted bun.
2. First up is a generous spread of salsa sauce. Mild or hot depending on your preference.
3. Add green leaf lettuce because the ruffles look so pretty.
4. Next up is some spicy, nut-free, and veggie-packed nacho cheese sauce.
5. Then, add a handful of fajita veggies aka roasted bell peppers and red onions.
6. Now comes the star of this burger the grilled portobello mushroom caps.
7. Finish it off, we some homemade guacamole.

What else can you add? 

To take it even further, we love to add another layer of grilled mushroom caps below the cheese sauce! So tasty and filling! And look how beautiful the layers are below! You can also add tomato slices instead or on top of the salsa sauce. Or avocado slices instead of guacamole.

FAQs and substitutions

Can you use other mushrooms?

Any other large caps mushrooms can be a good substitute, but usually, portobello is the most common and available type in stores.

How to store them?

You can store grilled mushrooms in a fridge for 3-4 days without any problem. We recommend assembling the burger before serving and not storing them as complete burgers.

Can you make them ahead of time?

You can store raw portobello mushrooms easily up to a week in the fridge, or at room temperature for 1-2 days. It is also best to marinate them overnight for the best flavor. The grilled mushroom caps can be stored in the fridge for up to 3-4 days. When you are ready to serve them, reheat them in a frying pan.

This vegan portobello mushroom burger recipe is vegan, so meat-free, dairy-free, and egg-free. It is also suitable for vegetarian, nut-free, and gluten-free diets. It is not suitable for an oil-free WFPB (whole foods plant-based) diet, as you cannot substitute olive oil in the marinade and get the same result as in the pictures.

More grilling recipes

You can browse through our vegan main course recipe or our 15-min quick & easy vegan meals collection or check out

UPDATED: This recipe was originally posted in May 2020. More info, tips, FAQs, and description were added and republished in June 2022.