Preheat oven to 475 degrees. Line baking sheet with aluminum foil.
Put flour and Panko bread crumbs in 2 separate dishes (or shallow bowls). Whisk egg whites until foamy in a third bowl.
Pat chicken dry with paper towels, roll in flour, dip in egg whites (or egg white substitute), then coat with Panko bread crumbs. Lay on baking sheet.
Bake until coating is brown and crisp, 12 to 15 minutes.
Make the sauce: whisk water, soy sauce, apricot jam, hoisin, corn starch, and vinegar together in a bowl. Heat vegetable oil in a 10-12 inch skillet over medium heat until shimmering. Add garlic, ginger, and pepper flakes, and cook until fragrant (1 minute). Add in soy sauce mixture, bring to simmer, and cook until thickened (2 minutes). Remove from heat, and cover to keep warm.
When chicken is cooked, return sauce to simmer, add cooked chicken, and toss to coat. (Optional: garnish with sesame seeds and cut scallions before serving)