Add 2-3 cups oil to a large bottom pot or pan over medium heat and let it heat up.
Make 2-3 deep slant cuts on each side of the fish.
Season generously with 1 teaspoon black pepper and 1 teaspoon salt.
Deep fry the fish until golden brown on both sides. It should be fully cooked. Fry for about 5 minutes on each side, depending on the thickness of the fish.
Remove the fish, drain the excess oil, and place it on a serving tray.
Reduce the oil to about 3 tbsp, Sauté the garlic, ginger and onion until fragrant for 1 minute.
Add the sugar, ketchup, carrots, and bell peppers and stir until they soften slightly.
Add the slurry (1 tablespoon cornstarch dissolved in 1 cup water) and vinegar. Stir and allow to simmer until the sauce thickens. You can add more water if needed for your desired consistency.