Vegetarian Portobello Mushroom and Avocado Burger

Gather the ingredients.

Lightly brush the individual mushrooms and onion slices with a bit of olive oil on both sides. Sprinkle the mushroom and onion slices with 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper; reserve the remaining salt and pepper.

Heat large a skillet or grill pan over medium heat until hot. Add the lightly oiled portobello mushrooms and allow them to cook until fully tender, 8 to 10 minutes, turning once.

Once the portobello mushrooms are fully cooked, transfer them to a plate, cavity-side up, and cover the mushrooms lightly with a paper towel or a kitchen cloth to keep them warm.

In the same skillet or grill pan, cook the onion slices until lightly golden brown on both sides, about 8 minutes, turning occasionally.

While the onions are cooking, start to prepare the avocado and yogurt sauce. In a small bowl, combine half of the avocado, yogurt, minced garlic, and the remaining 1/4 teaspoon of salt and black pepper. Using a fork, mash everything together until smooth and creamy.

To serve and assemble your portobello burgers, spoon the onions and the optional roasted red peppers into the grilled mushroom cavities, divided equally.

Spread the smooth avocado mixture on the bottom of each bun and then top each with the stuffed mushrooms. Top each burger with the remaining sliced avocado and any additional veggie burger fixings you'd like.