Preheat the oven to 400 degrees F. Place a baking rack on a sheet pan and arrange the bacon on the rack in a single layer. Bake for 15 to 25 minutes, until the bacon is browned and crisp. Drain on paper towels and set aside.
Combine the mayonnaise and ketchup in a small bowl and spread each slice of bread with about 1 tablespoon of the mixture and cover with a lettuce leaf. Place 3 slices of bacon on top of the lettuce and then add a layer of tomato slices on top of the bacon. Slice half of the breast of the rotisserie chicken in thick pieces and place a slice of chicken on top of the bacon. Sprinkle liberally with salt and pepper. Reserve the remaining chicken.
Spread each of the remaining 4 slices of bread with 1 tablespoon of the mayonnaise/ketchup mixture and place, dressing side down, on the sandwiches. Cut in half and serve.