Preheat oven to 375°F.
Put chicken breasts in a casserole dish. Add BBQ sauce to the chicken, dividing equally between them.
Add crushed pineapple to the chicken along with the bacon and chopped onions.
Cover the chicken breasts in Mozzarella cheese. Add extra pieces of pineapple to the top.
Bake until the chicken is fully cooked, about 25-30 minutes.
Sprinkle a small amount of chopped scallions over the chicken breasts.