01 - In a large mixing bowl, mash the drained black beans with a fork or potato masher until coarse and chunky, avoiding a fully pureed texture.
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 bowl with the mashed beans.
03 - Crack the egg into the bowl (or add the prepared flax egg) and mix thoroughly until all ingredients are evenly incorporated 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.
05 - Heat olive oil in a large skillet over medium heat. Cook the patties 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.
07 - Layer each bun with a cooked patty, lettuce leaves, tomato slices, pickles, and your preferred condiments. Serve immediately.