01 - In a large mixing bowl, mash the drained black beans with a fork or potato masher until coarsely broken down but not fully pureed. Some texture should remain for a hearty bite.
02 - Add the grated carrots, chopped mushrooms, diced red onion, corn kernels, minced garlic, parsley, rolled oats, breadcrumbs, smoked paprika, cumin, salt, and pepper to the bowl with the beans.
03 - Add the egg (or prepared flax egg) to the bowl and mix thoroughly until all ingredients are evenly distributed and the mixture holds together when pressed.
04 - Divide the mixture into 4 equal portions and shape each into a burger patty approximately 1 inch thick. Ensure edges are slightly smoothed to prevent crumbling during cooking.
05 - Heat olive oil in a large skillet over medium heat. 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 the skillet or under a broiler 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.