Pat the chicken pieces dry with paper towels and season with salt and pepper.
Place cornstarch and beaten eggs in separate shallow dishes. Dip each chicken piece in cornstarch, then in beaten eggs, shaking off excess.
Heat vegetable oil in a large skillet or wok over medium-high heat. Fry chicken in batches for 5-7 minutes, turning occasionally, until golden brown and cooked through. Drain on paper towels.
Whisk together cornstarch and water in a small bowl.
In a saucepan, combine pineapple juice, rice vinegar, brown sugar, ketchup, soy sauce, ginger, and garlic. Bring to a simmer over medium heat.
Add cornstarch slurry to the sauce and stir constantly until thickened, about 1-2 minutes.
Add fried chicken to the sauce and toss to coat. Serve immediately over rice or noodles, garnished with sesame seeds and green onions if desired.