Preheat the oven to 350°. Using a sheet pan or a casserole dish, add the chicken in a single layer. Brush with BBQ sauce. Bake for 25 minutes. Alternately, if you're only making a serving or two, it will be quicker to use an oven-proof skillet on the stovetop for this step. Brown the BBQ-brushed chicken over medium heat for about 6 minutes per side until cooked through
Turn the oven to broil. Top the cooked chicken with cheese, bacon, tomato, and scallions. Run under the broiler until the cheese is melted.