Preheat oven to 400 ℉.
Spread half of the EVOO in the bottom of a 13x9" casserole dish or oven-safe skillet. Place the butterflied chicken breasts in the dish or pan.
Fill the inside of each chicken breast with the sliced cheese, distributing it evenly. Then, top with half of the pepperoni, minced garlic, Italian seasoning, Parmesan cheese, marinara sauce, and shredded cheese.
Close each chicken breast over the pizza filling, securing with as many toothpicks as needed. Top the chicken breasts with the remaining EVOO, minced garlic, and Italian seasoning.
Bake at 400℉ for 25 minutes.
Remove from oven and top with the remaining marinara sauce, Parmesan, pepperoni, and shredded cheese.
Bake at 400℉ for an additional 20-30 minutes, until chicken is fully cooked through, and cheese begins to brown and bubble.
Allow to cool on wire rack for at least 5 minutes before serving.