In a large bowl, combine the mashed black beans, cooked quinoa, chopped mushrooms, chopped onion, minced garlic, soy sauce, nutritional yeast, smoked paprika, and ground black pepper. Mix until well combined.

Stir in the ground flaxseed (or breadcrumbs) to the mixture. This will help bind the ingredients together and provide structure to the patties.

Divide the mixture into 4 equal portions. With your hands, shape each portion into a patty, pressing firmly to ensure they hold together.

Heat olive oil in a skillet over medium heat. Once hot, add the patties and cook for 4-5 minutes on each side, or until golden brown and crispy.

Place the cooked patties on whole-grain or gluten-free buns. Top with your favorite toppings such as avocado slices, lettuce, tomato, pickled onions, and a drizzle of your preferred sauce.