Pat the fish fillets dry with paper towels. Cut into 1- to 1.5-inch pieces or bite-sized strips. Season evenly with 1 tsp salt, 1 tsp black pepper, and 1 tsp garlic powder.

Coat fish

In a shallow bowl combine 1 tbs cornstarch and 3 tbs all-purpose flour. Dredge each piece of fish in the flour mixture, shaking off excess so each piece has a light, even coating.

Pan-fry fish

Heat a large nonstick or stainless frying pan over medium-high heat and add 4 tbs vegetable oil. When oil is hot (shimmering but not smoking), add fish pieces in a single layer without crowding. Fry 2–3 minutes per side until golden and crisp and cooked through. Work in batches if needed. Transfer cooked fish to a paper-towel-lined plate and keep warm.

Sauce and finishing

Prep aromatics and sauce

While fish cooks, mince 3 garlic cloves, julienne 1 tbs ginger, thinly slice 1 fresh red chili, separate and slice 3 green onions (whites and greens kept separate), and thinly slice 1 small red bell pepper. In a small bowl whisk together 3 tbs ketchup, 2 tbs chili sauce, 1 tbs soy sauce, 1 tbs rice vinegar, 1 tbs brown sugar, and 3 tbs water until smooth. In a separate tiny bowl mix 1 tsp cornstarch with 1 tbs cold water to make a slurry.

Cook aromatics

Wipe the frying pan clean and return to medium heat. Add 1 tbs vegetable oil. When hot, add the minced garlic and julienned ginger and sauté 20–30 seconds until fragrant (don’t brown). Add the white parts of the green onions, sliced red chili, and sliced red bell pepper. Stir-fry 1–2 minutes until pepper starts to soften but remains crisp.

Add sauce and thicken

Pour the prepared sauce mixture into the pan and bring to a simmer. Stir and cook 1 minute, then pour in the cornstarch slurry while stirring continuously. Simmer another 30–60 seconds until the sauce thickens to a glossy, slightly sticky consistency. Taste and adjust seasoning—add up to 1/2 tsp salt or 1/2 tbs sugar if desired.

Combine fish and finish

Return the fried fish pieces to the pan and gently toss to coat evenly with the chilli sauce, being careful not to break the fish. Drizzle 1 tsp sesame oil (optional) and add the green parts of the green onions. Toss once to combine and warm through, about 30 seconds.

Serve

Transfer the chilli fish to a serving plate, garnish with chopped cilantro or parsley if using, and serve immediately with steamed rice or noodles.