Marinate the chicken: In a large bowl, mix olive oil, garlic powder, smoked paprika, and brown sugar. Add chicken breasts and coat evenly. Cover and refrigerate for at least 30 minutes.
Preheat the grill: Heat your grill to medium-high (375°F or 190°C).
Grill the chicken: Place marinated chicken on the grill and cook for 6-8 minutes until marked.
Flip and sauce: Turn chicken over, brush with BBQ sauce, and cook for another 6-8 minutes until the internal temperature reaches 165°F (75°C).
Rest and serve: Remove from grill and let rest for 5 minutes before serving with extra BBQ sauce if desired.