Preheat your grill to the highest setting.
I like to start with a chicken that has been at room temperature for about 20 minutes.
Take the chicken and spatchcock it – meaning you want to cut out the backbone with sharp kitchen shears and flatten it. It’s intimidating at first, but once you do it, it’s get easy! Here is a photo tutorial on it. Cut out the backbone of the chicken on both sides and press down with the heel of your hand (breaking the breastbone) to flatten the chicken as much as you can.
Stir together the brown sugar, paprika, garlic powder, salt and pepper. Sprinkle a bit on the underside of the chicken. Place the chicken skin-side up on a baking sheet or cutting board and sprinkle/run the spice mixture all over the skin. If you want, you can also sprinkle some under the skin, right on the breasts and thighs.
Once you’re ready to grill, turn off the heat in the center burner. We’re grilling with indirect heat here, so we don’t want that center burner on. Turn the side burners to medium heat. You want the heat of the grill to be around 350 to 400 degrees F. You may need to adjust your side burners to get to this temperature!
Place the whole chicken on the center of the grill (above the burner that is turned off), skin side up. Close the lid and grill for 50 to 60 minutes. After about 40 minutes, you can start brushing the top of the chicken with the BBQ sauce. I brush maybe two or three times, closing the lid after each time. You want the internal temperature of the chicken to read 160 to 165 degrees F before you remove it from the grill..
Remove the chicken and let it rest for 15 to 20 minutes. Slice and serve with the remaining BBQ sauce.