Coat the chicken: Toss chicken with soy sauce, cornstarch, and black pepper. Let it sit for 10 minutes.
Cook the chicken: Heat oil in a wok, fry chicken until golden, then set aside.
Sauté the vegetables: Stir-fry bell peppers, carrots, and pineapple until slightly softened.
Make the sauce: Mix ketchup, soy sauce, vinegar, brown sugar, honey, sesame oil, garlic, and ginger.
Combine everything: Return chicken to the wok, add noodles, and pour in the sauce.
Thicken the sauce: Stir in the cornstarch slurry and let the sauce coat everything.
Garnish and serve: Top with green onions and dig in immediately.