Clean and gut the fish. Season with salt and pepper to taste.
In a wide pan over medium heat, heat about 2-inch deep of oil. Add fish and cook, turning once or twice, until golden, crisp, and cooked through. Remove from heat and drain on paper towels. Keep warm.
In a pan over medium heat, heat about 1 tablespoon of oil. Add onions, garlic, and ginger and cook, stirring occasionally, until softened.
Add grated papaya and bell peppers and cook, stirring regularly, until tender yet crisp. Remove from pan and keep warm.
In a saucepan over medium heat, combine vinegar, sugar, and ketchup.
Season with salt and pepper to taste. Bring to a boil.
In a small bowl, combine cornstarch and water. Stir until smooth. Add to the pan and continue to cook, whisking continuously, for about 1 to 2 minutes or until sauce thickens.
Place fried fish on a serving platter and garnish with the vegetable mixture. When ready to serve, pour sweet and sour sauce on top.