Preheat oven to 400°F. Coat a baking dish with cooking spray, set aside.
Cut onion in half and slice thin. Cut bell peppers into bite size pieces. Seed and dice the jalapeño. Set aide.
In a bowl add chopped, bite-size chicken pieces and 2/3 cup of the barbecue sauce. Toss to coat, set aside to marinate for 15 minutes.
Arrange sliced onion in baking dish and top with marinated chicken pieces, bell peppers and pineapple. Brush remaining barbecue sauce on top, toss to coat and sprinkle on the diced jalapeño. Season with salt and pepper.
Bake uncovered for 30-35 minutes, or until internal temperature of chicken reads 165°F.