Give the pompano shallow cuts on each side. Season with salt. Dredge the fish with cornstarch. Shake off the excess starch. Fry in a pan with hot oil until golden and crispy on each side. Set aside.
In another bowl mix together vinegar, soy sauce, ketchup, sugar, salt and pepper to taste, cornstarch, and water. Mix well. Set aside.
In another pan with a bit of oil, saute ginger for a few minutes before sautéing garlic until aromatic. Saute in onions until soft. Add in carrots and bell peppers, saute for a minute.
Pour in the sauce and cook for 2 to 3 minutes. Pour the sauce all over the fried pompano. Garnish with green onions before serving.