01 - If using flaxseed, combine the ground flaxseed with water in a small bowl. Let the mixture rest for 5 minutes until it thickens into a gel-like consistency.
02 - Heat 1 tbsp olive oil in a skillet over medium heat. Add the onion, carrot, bell pepper, and garlic, then sauté for 4–5 minutes until softened. Fold in the spinach and cook until wilted. Remove from heat and set aside.
03 - Transfer the drained black beans to a large mixing bowl. Using a fork or potato masher, partially mash the beans while preserving some texture for a satisfying bite.
04 - Add the sautéed vegetables, rolled oats, breadcrumbs, tomato paste, smoked paprika, cumin, salt, pepper, and the prepared flax egg (or regular egg) to the mashed beans. Stir thoroughly until all ingredients are evenly distributed.
05 - Divide the mixture into 4 equal portions and shape each into a firm patty, approximately 3/4 inch thick.
06 - Heat the remaining olive oil in the skillet over medium heat. Cook the patties for 4–5 minutes per side until both sides are golden brown and the patties are cooked through.
07 - Serve the patties on toasted buns with your preferred toppings such as lettuce, tomato, avocado, or pickles.