01 - Mix ground flaxseed with water in a small bowl. Let sit for 5 minutes until thickened.
02 - In a large bowl, mash black beans with a fork or potato masher, leaving some texture for bite.
03 - Add red onion, garlic, rolled oats, breadcrumbs, smoked paprika, cumin, chili powder, salt, pepper, and the prepared flax egg. Mix until fully combined.
04 - Divide the mixture into 4 equal portions and shape into patties about 1 inch thick.
05 - Heat olive oil in a large skillet over medium heat. Cook patties for 5–6 minutes per side until crispy and heated through.
06 - While patties cook, combine vegan mayo, chipotle peppers, lime juice, and salt in a small bowl. Whisk until smooth.
07 - Lightly toast burger buns in the skillet or toaster for added texture.
08 - Spread chipotle mayo on bottom bun, add black bean patty, avocado slices, tomato, lettuce, and red onion. Top with remaining bun half.