In a bowl, season fish fillets with salt and pepper to taste and set aside.
In a separate bowl, beat egg well.
In another bowl, add flour.
To assemble, dredge fish fillets over flour mixture until coated. Dip fish in the beaten eggs then transfer back to flour mixture and coat well.
In a skillet over medium heat, add 2 cups of oil. Deep fry battered fish fillets in batches if needed. Turn them once or twice until golden brown or cooked through.
Remove from the pan and drain fish fillets with paper towel.
In a bowl, combine pineapple juice, vinegar, ketchup, brown sugar, cornstarch and salt. Stir until smooth and set aside.
In a wok, heat about 1 tablespoon of oil. Sautè onion, garlic and ginger until fragrant. Add bell peppers and stir for 1 minute.
Pour in sweet and sour sauce and bring it to boil for 2-3 minutes until thickened.
Gently toss fried fish fillets and mix just until coated with sauce. Serve hot and enjoy.