Are you looking for a tasty meat-free alternative to hamburgers? These delicious Portobello Burgers with Pesto Mayonnaise will hit the spot! This hearty vegan sandwich is topped with homemade mayo, caramelized onions, a juicy portobello mushroom and slice of tomato. They are easy to make, full of flavor and perfect for a summer barbecue!

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What do I need to make the Portobello Mushroom Burgers and Pesto Mayonnaise?

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How do I make the Portobello Burgers?

There are just a few simple steps to create these tasty plant-based sandwiches. This recipe is easy to make; however it does require time for the mushrooms to marinate and to caramelize the onions. So, plan a little ahead of time when making them.

Step 1: Prepare the marinade

Prepare the marinade by combining the balsamic vinegar, soy sauce, Worcestershire sauce, olive oil, garlic powder, smoked paprika and salt. Using a cooking brush, brush the marinade on both sides of the mushrooms. Let them marinate for 30 minutes, with the cap side down.

Step 2: Caramelize the onions

Remove peel from onions and cut into thin slices. Place a large skillet over medium heat and add in 2 tablespoons of olive oil. When olive oil is hot, add in onion slices and cook over medium heat for approximately 30 minutes, until they are golden brown and caramelized. Keep warm and set aside.

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Pro Tip: Sprinkle salt over onions after 10 minutes. Stir frequently to prevent burning, but also do not over stir the onions as they need to brown.

Step 3: Prepare the Pesto Mayonnaise

To make the pesto mayonnaise, blend vegan mayonnaise, pecans, basil, nutritional yeast, garlic, salt and olive oil with an immersion blender, food processor or regular blender. Process until smooth.

Step 4: Make the Portobello Burgers

Cook the portobellos cap side down over medium heat in a skillet or on the grill until tender. It will take about 8 to 10 minutes. Make the burgers by adding pesto mayonnaise and caramelized onions to the base of the bun. Then, top with a juicy portobello and slice of tomato. Serve warm and enjoy!

What can I serve with the Vegan Mushroom Burgers?

These delicious plant-based burgers can be served with just about anything! If you are sticking to vegan sides, give these recipes a try:

Portobello Burgers with Pesto Mayonnaise

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Servings:

Calories: 378kcal

Ingredients

Portobello Burgers:

4 large portobello mushrooms
4 hamburgers rolls
2 onions thinly sliced
1 large tomato sliced
2 tablespoon olive oil

Marinade:

1 tablespoon balsamic vinegar
1 tablespoon soy sauce
1 tablespoon Worcestershire sauce
½ tablespoon olive oil
½ teaspoon garlic powder
1 teaspoon smoked paprika
¼ teaspoon salt

Pesto Mayonnaise:

⅓ cup vegan mayonnaise
⅓ cup pecans can substitute with pine nuts or walnuts
1 cup packed fresh basil leaves
1 tablespoon nutritional yeast
2 garlic cloves
¼ teaspoon salt
2 tablespoon olive oil

Instructions

Prepare the marinade:

Clean portobellos and remove the stalks.
Prepare the marinade by combining the balsamic vinegar, soy sauce, Worcestershire sauce, olive oil, garlic powder, smoked paprika and salt.
Using a cooking brush, brush the marinade on both sides of the mushrooms. Let them marinate for 30 minutes, with the cap side down.

Caramelize the onions:

Cut onions into thin slices.
Place a large skillet over medium heat and add in 2 tablespoons of olive oil.
When olive oil is hot, add in onion slices and cook over medium heat for approximately 30 minutes, until they are golden brown and caramelized. Remove from heat and set aside.
* Tip: Sprinkle salt over onions after 10 minutes. Stir frequently to prevent burning, but also do not over stir the onions as they need to brown.

Make the Pesto Mayonnaise

To make the pesto mayonnaise, blend vegan mayonnaise, pecans, basil, nutritional yeast, garlic, salt and olive oil with an immersion blender, food processor or regular blender. Process until smooth.

Make the burgers:

Cook the portobellos cap side down over medium heat in a skillet or on the grill until tender. It will take 8-10 minutes.
Make the burgers by adding pesto mayonnaise and caramelized onions to the base of the bun. Then, top with a juicy portobello and slice of tomato.