Preheat the oven to 190°C.
With a sharp knife, slice a deep pocket along the side of each chicken breast, taking care not to cut through completely.
Fill each chicken breast with equal portions of sliced roasted red peppers, fresh spinach, and shredded mozzarella cheese.
Use toothpicks to close the openings as needed to keep the filling intact.
Combine olive oil, garlic powder, Italian seasoning, salt, and ground black pepper in a small bowl. Brush the mixture evenly over both sides of each stuffed chicken breast.
Arrange the prepared chicken breasts in a baking dish and bake for 25–30 minutes, or until the chicken is thoroughly cooked and no longer pink in the center.
