Sprinkle fish fillet with salt and pepper, then coat with flour.
Heat 2 tablespoon oil in a frying pan on medium high and pan fry fish fillets until golden brown on both sides, about 2 minutes per side. Set aside in a serving plate.
Heat about 2 tablespoon oil in a frying pan (use the same unwashed pan to fry fish) on medium high heat and sauté garlic and onion until fragrant, about 3 minutes.
Add tomato. Mix well, and cook for another minute.
Add Thai sweet chili sauce, water, chili sauce, vinegar, fish sauce, salt, and sugar. Mix well. Bring to a boil. Adjust taste as needed.
Thicken sauce with cornstarch solution. Turn off heat once the sauce has thickened.
Add chopped cilantro and scallions into the sauce. Mix well. Pour the sauce over the fried fish. Serve immediately.
