01 - Mash black beans in a large bowl using fork or potato masher until mostly smooth, leaving some chunks for texture.
02 - Add chopped red onion, garlic, breadcrumbs, oats, egg, cumin, smoked paprika, chili powder, salt, pepper, and cilantro. Mix until thoroughly combined.
03 - Divide mixture into 4 equal portions and shape into burger patties.
04 - Heat olive oil in non-stick skillet over medium heat. Add patties and cook 4-5 minutes per side until golden and heated through. Add cheese slices during last minute if using; cover to melt.
05 - Lightly toast burger buns until golden.
06 - Spread mayonnaise and ketchup on buns. Layer with lettuce, black bean patty, tomato, avocado, red onion, and pickles if desired. Top with remaining bun.
07 - Serve hot with preferred sides.