Start by mixing the coating for your fish. In a large bowl, combine beaten egg, cornstarch, salt, ginger powder, and water. Mix until smooth. Add your cream dory pieces and coat each piece well. Let this rest for 15 minutes.
While waiting, get your sauce ready. In a bowl, mix water, pineapple juice, brown sugar, vinegar, ketchup, soy sauce, and sesame oil. Set this aside. In a small separate bowl, mix 1 tablespoon cornstarch with ¼ cup water until smooth.
Next, prepare your vegetables. Cut your bell pepper into squares, onions into quarters, slice your carrots diagonally, mince the garlic, and cut ginger into thin strips. Keep these ready.
Heat enough oil for deep frying in a large pan. Once hot (around 350°F), fry your coated fish pieces until golden brown, about 3-4 minutes. Don't overcrowd the pan. Once done, place on paper towels to drain excess oil.
Using a clean pan, heat 2 tablespoons of oil. Add ginger and garlic, cooking until fragrant. Add onions and cook for 1 minute. Add bell peppers, carrots, and pineapple chunks. Cook for 2-3 minutes until vegetables are crisp but still colorful. Remove from pan and set aside.
In the same pan, pour your prepared sauce mixture. Let it come to a boil over medium heat. Once boiling, slowly pour in your cornstarch-water mixture while stirring constantly. Keep stirring until the sauce thickens, about 2-3 minutes.
Finally, add back your fried fish and cooked vegetables to the pan. Gently toss everything in the sauce until well coated. Serve hot with steaming rice.
Remember: For the crispiest fish, serve right away. If you need to wait before serving, keep the fried fish separate from the sauce and combine only when ready to eat.