01 - Combine ground flaxseed with water in a small bowl and let it thicken for 5 minutes.
02 - In a large bowl, mash black beans with a fork or potato masher until mostly smooth but still slightly chunky.
03 - Add rolled oats, gluten-free breadcrumbs, chopped red onion, minced garlic, flax egg, tomato paste, smoked paprika, ground cumin, chili powder, salt, and black pepper to the mashed beans. Mix thoroughly until evenly combined.
04 - Shape the mixture into four equal patties, pressing firmly to ensure they hold together.
05 - Heat olive oil in a large skillet over medium heat. Cook each patty for 5 to 6 minutes per side until browned and heated through.
06 - In a small bowl, mix vegan mayonnaise, finely chopped chipotle peppers, adobo sauce, lime juice, and a pinch of salt. Adjust seasoning to preference.
07 - Toast vegan burger buns if desired.
08 - Spread chipotle mayo on each bun, place a black bean patty on the bottom bun, then add lettuce, sliced tomato, red onion, and optional pickles. Serve immediately.