01 - Mash black beans in a large bowl using fork or potato masher until mostly smooth, leaving some chunks for texture.
02 - Mix in red onion, garlic, breadcrumbs, oats, egg, cumin, smoked paprika, chili powder, salt, pepper, and cilantro until well combined.
03 - Divide mixture into 4 equal portions and form into burger patties.
04 - Heat olive oil in non-stick skillet over medium heat. Cook patties 4-5 minutes per side until golden and heated through. Add cheese slices during final minute if using; cover to melt.
05 - Lightly toast burger buns.
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.