In a large mixing bowl, whisk the egg with soy sauce. Add the chicken pieces and toss to coat. Let them marinate briefly while you set up the coating.
In a shallow dish, combine flour, 1 cup cornstarch, salt, and pepper. Dredge the marinated chicken pieces in the coating, pressing gently so the mixture sticks.
Heat about 1 inch of oil in a heavy skillet or Dutch oven to 350°F (175°C). Fry the chicken in batches until golden and crisp, about 3–4 minutes per side. Transfer to a rack or paper towels to drain. Reserve 2–3 tablespoons of oil for the sauce if needed.
In a large skillet, sauté the bell peppers and pineapple chunks over medium heat for 2–3 minutes until just tender-crisp.
In a small bowl, whisk together ketchup, vinegar, brown sugar, soy sauce, garlic powder, ginger, and 2 tablespoons water. Pour into the skillet with the peppers and pineapple.
Whisk 1 tablespoon cornstarch with 2 tablespoons water to create a slurry. Stir the slurry into the sauce and simmer until thickened to a glossy coating, about 1–2 minutes.
Return the fried chicken to the pan and toss to coat evenly with the sauce. Cook for an additional 1–2 minutes to meld the flavors.
Taste and adjust sweetness or tang with a touch more vinegar or sugar, if you like. Serve immediately over steamed rice or alongside noodles.