1. FOR THE CHICKEN: Adjust oven rack to upper-middle position and heat oven to 475 degrees. Set wire rack inside rimmed baking sheet and spray with oil spray. Process cornflakes in food processor until finely ground, about 10 seconds. Place flour in shallow dish. Whisk egg whites in second shallow dish until foamy. Place cornflake crumbs in third shallow dish.
2. Pat chicken dry with paper towels. Dredge chicken in flour; dunk in egg whites; then coat with cornflake crumbs, pressing to adhere. Transfer to prepared wire rack. Spray chicken lightly with oil spray. Bake until chicken is cooked through and coating is brown and crisp, 12 to 15 minutes.
3. FOR THE SAUCE: While chicken cooks, whisk water, soy sauce, jam, hoisin, cornstarch, and vinegar together in bowl. Heat oil in 12-inch skillet over medium heat until shimmering. Add garlic, ginger, and pepper flakes and cook until fragrant, about 1 minute. Whisk in soy mixture, bring to simmer, and cook until thickened, about 2 minutes. Remove from heat, cover, and keep warm.
4. When chicken is cooked, return sauce to simmer over medium-low heat. Add cooked chicken and toss to coat.