Combine kidney beans and black beans in a large bowl; partially mash with a fork.

Add breadcrumbs, corn, onion, and egg; stir until well blended.

Form bean mixture into 4-6 patties.

Heat oil in a large nonstick skillet over medium high heat.

Add patties to pan; cook 4 minutes on each side or until crisp and beginning to brown.

To prepare ketchup, combine all ingredients and sir with a whisk.

Spread 1 tablespoon ketchup on the bottom of a bun; to with patty, 1 lettuce leaf and 1 tomato slice (if desired), and to half of bun.