01 - Combine ground flaxseed and water in a small bowl. Stir and allow to thicken for 5 minutes.
02 - In a large bowl, mash the drained black beans with a fork or potato masher, retaining some texture.
03 - Add oats, diced onion, garlic, bell pepper, smoked paprika, cumin, chili powder, salt, black pepper, cilantro, and flax egg to the mashed beans. Mix thoroughly until combined.
04 - Divide the mixture into four equal portions and form each into a compact burger patty.
05 - Heat a non-stick skillet or grill pan over medium heat. Lightly oil if desired. Cook each patty for 5 to 6 minutes per side until browned and heated through.
06 - Whisk together vegan mayonnaise, chopped chipotle pepper, adobo sauce, lime juice, garlic powder, and salt in a small bowl.
07 - Toast the vegan burger buns lightly if preferred.
08 - Spread chipotle lime mayo on the buns, layer with lettuce, tomato, red onion, and avocado, then top with the black bean patty. Serve immediately.