Preheat the oven to 400°F. Lightly coat a 15x10x1-inch baking pan with cooking spray. In a shallow bowl, whisk the egg until it's well beaten. In a separate bowl, combine the bread crumbs, Parmesan, salt, pepper and garlic powder. Dip a chicken breast in the beaten egg, allowing any excess to drip off. Dip the breast into the bread crumb mixture, patting it gently to help the crumb coating adhere. Repeat with the remaining chicken, then place the chicken breasts in the middle third of the sheet pan, and spritz them with cooking spray.
Bake the chicken for 10 minutes, then remove the pan from the oven. Spread the broccoli florets in a single layer along both sides of the pan (if you’re using frozen broccoli, separate the pieces). Return the pan to the oven, bake for another 10 minutes, then remove the pan again.
Preheat the broiler. Pour the marinara sauce evenly over the chicken breasts, then top them with shredded mozzarella. Broil the chicken and broccoli 3 to 4 inches from the heat until the cheese is golden brown and the broccoli is tender, three to five minutes. Before serving, sprinkle on the basil leaves, if desired.
