Preheat your oven to 375F and move the rack to the middle position.
Season both sides of each piece of chicken with the garlic powder and salt & pepper.
Add the oil to a large skillet over medium-high heat. Once the pan is hot, sear the chicken for 5 minutes/side.
Transfer the chicken to a 9x13 casserole dish. Pour in the pizza sauce and spoon it evenly over/around the chicken.
Sprinkle the mozzarella over each chicken breast.
Top the chicken breasts with the tomato slices and pepperoni.
Bake, uncovered, for 20 minutes. If your chicken breasts are on the smaller side, try 15 minutes, and very large ones may need 25 minutes.
Let the chicken rest for 5 minutes prior to serving (this will ensure it's juicy). The chicken's temperature will continue rising a few degrees as it rests. Chicken is safe to eat at 165F.
Sprinkle with fresh basil and enjoy!