In a food processor, combine chopped mushrooms and walnuts until finely chopped.

Transfer to a mixing bowl and add bread crumbs, egg, garlic powder, onion powder, salt, and pepper.

Mix until well combined and form into patties.

Heat a skillet over medium heat and cook the patties for about 5-7 minutes on each side until golden brown.

Place the cooked patties on buns and top with cheese, lettuce, and tomato.