The best fish to use is white fish with slightly fatty and firm flesh. The blubberlip snapper is the best option to go with due to its texture and flavour profile.
Mix the fish coating ingredients in a tray or plate that is large enough to hold one fish fillet.
Mix the sauce ingredients in a big bowl and stir well.
Score the fish by slicing 2.5cm cross hatch pattern across the flesh. If using skin-on, cut the skin but not through it.
In a work, heat up oil over medium-high heat until it reaches 190C. Coat as much fish as you can fry at a time. Place the fish skin-side down in the tray with cornstarch mixture. Use a spoon to add more mixture on top. Carefully lift the fillet to shake off extra cornstarch and make sure that there’s cornstarch between the diamond cuts.
Once the fish is coated, gently lay into the heated oil. Cook for 4-5minutes without touching the fish until it turns golden brown. Flip and cook the other side for another 2-3minutes. Once done, transfer the fillet to a plate to drain the excess oil.
In a medium sized frying pan, heat 1 teaspoon of oil over medium heat until hot. Add ginger and garlic and stir for 30seconds till it releases its fragrance. Add onions and continue stirring.
Stir the sauce mixture again to thoroughly dissolve the cornstarch and pour it into a pan. Stir and bring the sauce to a boil.
As soon as the sauce thickens, add the bell peppers and stir a few times more till it thickens. Immediately transfer to a bowl and serve.