Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).
Pat chicken breasts dry with paper towels and season both sides with salt, pepper, and garlic powder.
Heat olive oil in a large oven-safe skillet or baking dish.
Arrange chicken breasts in the dish in a single layer.
Spread a generous layer of barbecue sauce over each chicken breast.
Place 1 to 2 pineapple rings on top of each breast and scatter sliced red onions around the chicken.
Brush the top of the pineapples with the remaining barbecue sauce.
Bake for 20 to 25 minutes, or until the internal temperature of the chicken reaches 165 degrees Fahrenheit (74 degrees Celsius).
Remove from oven and let rest for 5 minutes before serving.
Garnish with fresh cilantro.