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