If making homemade BBQ sauce: follow the my sweet BBQ sauce recipe. It makes about 2 cups. If you're not making your own BBQ sauce, skip to the next step.
Preheat oven to 425 F. Get the oven rack adjusted to the middle position.
Spatchcock the chicken: Using strong kitchen shears, cut through the backbone of the chicken and remove it, along with any little bones that may be sticking out. With the lower side of the palm of your hands, press down the chicken breast until flattened. Thoroughly pat dry the chicken. Note: for more step-by-step instructions and pictures, check out my how to spatchcock a chicken post.
Season chicken with salt, black pepper, and garlic powder. Rub some olive oil (about 2-3 tablespoons) along with the seasoning, all over the chicken on both sides. Clip off the wing tips or hide them under the skin so that they don't burn. Transfer prepared chicken to a large and sturdy sheet pan.
Set aside 1/2 cup of the BBQ sauce for brushing the chicken. Reserve the rest of the BBQ sauce for serving.
Roast the chicken for about 35 mins. Remove from oven and brush with some BBQ sauce, and return to oven for 10 minutes. One more time, remove from oven and brush with more BBQ sauce, and return to oven for another 10 minutes. It should be about 55 minutes total in the oven, or until internal temperature reaches 165 degrees F. Remove from oven and let the chicken rest for 10 minutes before serving.
Cut up the chicken and serve with the reserved BBQ sauce. Enjoy!