Preheat oven to 375°F.
Spread half (¾ cup) of marinara sauce evenly in the bottom of a 9x13 baking dish.
Arrange the chicken breasts in a single layer in the baking dish.
In a mixing bowl, combine ricotta cheese, parmesan cheese, ½ cup mozzarella, egg, garlic powder, Italian seasoning, salt, and black pepper until smooth.
Divide the cheese mixture evenly and spread over each chicken breast.
Spoon the remaining ¾ cup marinara sauce over the cheese-coated chicken breasts, spreading gently without mixing.
Cover the dish with aluminum foil and bake for 25 minutes.
Remove the foil, sprinkle the remaining 2 cups mozzarella evenly on top, and bake uncovered for 15-20 minutes, or until the cheese is melted and chicken reaches 160–165°F.
Optionally, broil the cheese for 2-3 minutes to brown, watching carefully to prevent burning.
Let the chicken rest for 3-5 minutes before garnishing with fresh basil if desired.