Whisk the sauce: In a measuring cup, combine sugar, honey, apple cider vinegar, ketchup, soy sauce, garlic, and optional ginger. Set aside.
Set up coating: In a shallow dish, mix the cornstarch and flour. In a separate bowl, beat the eggs.
Coat the chicken: Dip chicken pieces in egg, let excess drip, then press into the cornstarch–flour mixture to fully coat. Arrange on a wire rack and let stand 5 minutes to help the crust adhere.
Heat the oil: Pour about 1 inch of vegetable oil into a heavy skillet or Dutch oven and warm over medium to medium-high heat until the oil reaches 350°F.
Fry in batches: Add half the chicken and cook 4–5 minutes total, turning once, until deep golden and cooked through (165°F). Transfer to a wire rack set over a sheet pan. Repeat with remaining chicken.
Stir-fry produce: Carefully pour off all but 1 tbsp oil. Add pineapple and cook 45–60 seconds to lightly caramelize. Add peppers and onion; stir-fry 2–3 minutes until crisp-tender.
Thicken the sauce, then combine: Reduce heat to medium. Give the sauce a stir and pour it into the pan. Simmer 1–2 minutes until glossy and slightly thickened. Add the chicken and toss 30–60 seconds to coat evenly.
Rest and serve: Take off the heat and let stand 1 minute so the coating grabs the sauce. Serve hot with sesame seeds or sliced green onions, if desired.