Place the beans into a food processor with vinegar, BBQ sauce, breadcrumbs, flaxseed, and seasonings. Pulse for about 1 minute until the mixture holds together.

Divide the mixture into 2 equal portions and form them into patties.

Heat oil in a skillet over medium heat.

Carefully place the patties into the hot oil and sear each side until slightly brown and crispy, about 4 minutes per side.

Heat another non-stick pan over medium heat. Add buns and toast until both sides are warmed through and lightly crispy.

Spread BBQ sauce on the insides of the buns, add a bean patty, onion, tomato slices, and lettuce leaves.