Preheat oven to 400. Add shredded chicken & BBQ sauce to saucepan over medium heat. Add garlic & onion powders. Cook just until heated through.
Meanwhile heat grill or grill pan to medium high heat.
Sprinkle salt over each pineapple slice and add to grill. Cook about 3-5 minutes, until it good grill marks appear. Flip over and cook the other side the same. Set aside.
On a foil lined baking sheet, place the open buns and layer bun, BBQ chicken, pineapple and cheese and then top of bun. Cook in oven for 5 minutes until cheese is melty and bun is toasty.