01 - Place the drained and rinsed black beans in a large mixing bowl. Using a potato masher or fork, mash the beans until coarsely broken down but not fully pureed — some texture should remain.
02 - Add the grated carrots, chopped mushrooms, diced red onion, corn kernels, minced garlic, chopped parsley, rolled oats, breadcrumbs, smoked paprika, ground cumin, salt, and black pepper to the mashed beans.
03 - Crack the egg into the bowl (or add the prepared flax egg). Stir thoroughly until all ingredients are evenly distributed and the mixture holds together when pressed.
04 - Divide the mixture into 4 equal portions. Shape each portion into a patty approximately 1 inch thick, pressing firmly so they hold their shape.
05 - Heat the olive oil in a large skillet over medium heat. Carefully place the patties in the pan and cook for 4 to 5 minutes per side until golden brown and cooked through.
06 - Toast the burger buns in a dry skillet or oven until lightly golden on the cut sides.
07 - Layer each bottom bun with a lettuce leaf, a cooked patty, tomato slices, pickles, and your preferred condiments. Cap with the top bun and serve immediately.