Preheat your grill to medium-high heat.
Pound the chicken breasts to an even thickness for even cooking. Season both sides with salt, pepper, garlic powder, and Italian seasoning.
Drizzle olive oil over the chicken to prevent sticking. Place the chicken on the grill and cook for about 6-7 minutes on each side, or until the internal temperature reaches 165°F.
In the last few minutes of grilling, spoon marinara sauce over each chicken breast, then top with mozzarella and Parmesan cheese. Close the grill lid to melt the cheese, about 2-3 minutes.
Remove the chicken from the grill and let it rest for 5 minutes. Garnish with fresh basil, if desired, before serving.