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, 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) and mix thoroughly until all ingredients are evenly distributed and the mixture holds together when pressed. Adjust with additional breadcrumbs if too wet.
04 - Divide the mixture into 4 equal portions and shape each into a burger patty approximately 1 inch thick. Place on a plate or sheet pan lined with parchment paper.
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 both sides are golden brown and the patties are cooked through.
06 - While the patties rest, toast the burger buns cut-side down in the same skillet or under a broiler until lightly golden.
07 - Layer each bottom bun with a lettuce leaf, a cooked patty, tomato slices, pickles, and ketchup or your preferred sauces. Cap with the top bun and serve immediately.