Place the first 6 ingredients in a food processor. Pulse until the beans are well blended. Transfer the mixture to a bowl. Mix in the onion, bell pepper, cilantro and salt. Line a plate with plastic wrap. Place the cornmeal on a second plate. Using cold water moistened hands, shape 1/3 of the mixture for each patty into 3/4" thick patties. Coat each one in cornmeal and set on a plate lined with plastic wrap (patties can be made several hours in advance; covered and stored in fridge until needed).
Heat the oil in a large, non-stick skillet set over medium heat. Add the patties and cook 3 to 4 minutes per side, or until heated through and golden. Place a lettuce leaf on the bottom of each bun; set on the patties. Top with salsa and cheese and serve.