In a mixing bowl, mash the black beans with a fork until mostly smooth, leaving some chunks for texture.

Add the bread crumbs, chopped onion, minced garlic, cumin, smoked paprika, salt, black pepper, and egg (if using). Mix until well combined.

Divide the mixture into 4 equal portions and shape each portion into a patty.

Heat olive oil in a skillet over medium heat. Cook the patties for about 5 minutes on each side, or until they are golden brown and heated through.

Place each patty on a bun and top with lettuce, tomato, avocado, and any additional toppings you prefer.