Heat the oven to 425°F. Set a wire rack inside a rimmed baking sheet and coat it with cooking spray.
Pat the tenderloins dry with paper towels (this is what makes the coating stick — don't skip it).
Put the beaten egg in a shallow bowl. In a second shallow bowl, mix the panko, Parmesan, and garlic powder.
Dip each tenderloin in egg, let the excess drip off, then press firmly into the panko mixture on both sides.
Arrange on the wire rack with space between each piece. Lightly spray the tops with cooking spray.
Bake 9 minutes, flip, and bake 8 to 10 minutes more, until deep golden and the centers read 165°F on a meat thermometer.