Rinse and prepare beans: Rinse and sort beans according to package directions.

Cook onions and bacon: Heat oil in a large skillet over medium-high. Add onion, bell pepper, and, if desired, bacon; cook, stirring occasionally, until onions are tender, about 8 minutes. Add garlic, and cook, stirring often, until fragrant, about 30 seconds.

Cook beans: Transfer onion mixture to a 6-quart slow cooker; add beans, jalapeño, chicken broth, salt, brown sugar, cumin, pepper, and oregano. Cover and cook on LOW until beans are tender, about 6 hours.

Prepare Comeback Sauce: Stir together mayonnaise, sweet chili sauce, smoked paprika, ketchup, hot sauce, and Worcestershire sauce.

Blend beans: Process 1 ½ cups drained cooked black beans and ¼ cup mayonnaise mixture in a food processor until smooth, about 10 seconds.

Form patties: Stir together pureed bean mixture, 2 cups drained Black Beans, beaten egg, panko, grated yellow onion, and 1 teaspoon kosher salt in a large bowl. Cover and chill mixture 30 minutes. Form bean mixture into 4 (8 oz.) patties; chill 30 minutes.

Cook burgers: Heat 2 tablespoons olive oil in a large cast-iron skillet over medium-high and cook patties until heated through and a crust forms, about 4 minutes per side.

Assemble burgers: Top each patty with 1 slice of Muenster cheese; cook until melted. Divide remaining mayonnaise mixture evenly among buns; add 1 patty, 1 butter lettuce leaf, and 2 tomato slices to each bun.