Preheat oven to 375°F (190°C).
Line a baking sheet with parchment paper or lightly coat with non-stick cooking spray.
Pat the chicken breasts dry with paper towels and arrange them on the prepared baking sheet in a single layer.
In a medium mixing bowl, combine the mayonnaise, Parmesan cheese, garlic powder, salt, and pepper. Stir until a consistent paste forms.
Spread the mayonnaise mixture evenly over the top and sides of each chicken breast using a spatula or spoon.
Bake for 25 to 30 minutes, or until the internal temperature of the thickest part of the breast reaches 165°F (74°C) on an instant-read thermometer.
Optional: Broil for 1-2 minutes at the end of the cooking time to brown the topping.
Remove from oven and let the chicken rest for 5 minutes before serving to ensure maximum moisture retention.