Preheat oven to 375°. Spray a 9x11 baking dish with non stick cooking spray. Set aside.
In a large bowl, mix together bbq sauce and garlic powder. Add chickn breasts to bowl and mix around with hands to coat each breast evenly.
Place chicken breasts in baking dish side to side. Pour any remaining bbq sauce on top of chicken and spread around evenly.
Bake in preheated oven uncovered for 30 minutes.
Take chicken out of oven and add cheese, jalapeños and onions on top of chicken evenly.
Place back in oven and bake for an additional 7-10 minutes, or until middle of chicken reaches 165°. Depending on thickness of chicken breasts, it may take more or less time.
Enjoy!