1. Preheat the oven to 375°F (190°C).

2. Pat the chicken breasts dry with paper towels. Using a sharp knife, carefully slice horizontally through the thickest part of each breast to create a pocket, leaving about a ½-inch hinge on one side. Alternatively, place each breast between two pieces of plastic wrap and pound to ½-inch thickness.

3. In a small bowl, combine garlic powder, onion powder, Italian seasoning, salt, and black pepper. Generously season both the inside and outside of each chicken breast with the spice mixture.

4. Open each seasoned chicken breast like a book. On one half, spread 1-2 tablespoons of marinara sauce, leaving a small border. Sprinkle about ¼ cup of shredded mozzarella over the sauce. Add mini pepperoni or other toppings if desired. Do not overstuff.

5. Fold the other half of the chicken over the filling to seal. Secure edges with toothpicks if needed.

6. Heat olive oil in a large oven-safe skillet over medium-high heat. Place stuffed chicken breasts in the skillet and sear for 2-3 minutes per side until golden brown.

7. Transfer the skillet to the preheated oven, or place the stuffed chicken in a lightly greased baking dish if not seared. Bake for 20-25 minutes until the chicken reaches an internal temperature of 165°F (74°C). During the last 5 minutes, you can sprinkle extra mozzarella on top.

8. Remove from the oven and let rest for 5 minutes. Remove toothpicks, garnish with fresh parsley, and serve.