Pat dry the whole chicken with paper towel or a kitchen towel. Turn the chicken breast side down and use kitchen sheers or a sharp knife to cut on both sides of the back bone. Remove the bone and flip the chicken over. Press hard to flatten the chicken.
In a small bowl, combine the ingredients for the spice rub: brown sugar, paprika, garlic powder, cayenne pepper, salt, and pepper.
Sprinkle the spice rub generously over the chicken, ensuring it is evenly coated.
Pour the oil over the chicken and rub it in to coat the chicken thoroughly. Allow the chicken to marinate for at least 30 minutes to enhance the flavors.
Preheat a grill pan or outdoor grill over medium heat.
Add the marinated chicken to the grill and cook for approximately 40-45 minutes, up to an hour, turning the chicken occasionally to ensure even cooking and to achieve beautiful grill marks and an internal temperature of 165F.
Once the chicken is cooked through and reaches a safe internal temperature, transfer it to a plate.
Garnish the grilled chicken with chopped parsley and serve with lemon wedges on the side.
Serve the flavorful chicken with some grilled veggies on the side.