Place frozen peaches and onion slices on a large rimmed baking sheet; season with salt and pepper to taste. Sprinkle with ginger, soy sauce, one tablespoon of olive oil, sesame oil, and red pepper flakes, and toss to coat.
Rub chicken breasts with remaining teaspoon of olive oil, and season with salt and pepper to taste. Arrange chicken skin-side up among peaches and onions.
Roast until chicken is opaque throughout and registers 160 on a thermometer inserted in the thickest part of the breast, about 25 to 30 minutes.