01 - If using flaxseed, combine ground flaxseed with 3 tablespoons of water in a small bowl. Let the mixture rest for 5 minutes until it thickens into a gel-like consistency.
02 - Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the chopped onion, grated carrot, diced bell pepper, and minced garlic. Sauté for 4 to 5 minutes until the vegetables are softened. Stir in the chopped spinach and cook until wilted. Remove the skillet 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 leaving some texture intact for a hearty bite.
04 - Add the sautéed vegetables, rolled oats, breadcrumbs, tomato paste, smoked paprika, ground cumin, salt, black pepper, and the prepared flax egg (or regular egg) to the mashed beans. Mix thoroughly until all ingredients are evenly incorporated.
05 - Divide the mixture into 4 equal portions and shape each into a firm patty approximately 3/4 inch thick.
06 - Heat the remaining tablespoon of olive oil in the skillet over medium heat. Place the patties in the skillet and cook for 4 to 5 minutes per side until golden brown and heated through completely.
07 - Serve the patties on toasted buns with your preferred toppings such as crisp lettuce, sliced tomato, avocado, or pickles.