First, prepare the fish. Pat dry using paper towels.
Trim the fins and tail using kitchen shears.
Make a few diagonal cuts on both sides.
Rub each side with ½ teaspoon salt and ½ teaspoon turmeric. Rub the inside with the remaining salt and turmeric.
Preheat your air fryer, 3 to 5 minutes.
While the air fryer is preheating, coat both sides of the fish with the cornstarch.
Spray with cooking oil on both sides, not leaving any dry spots of cornstarch.
When the air fryer is done preheating, lightly brush the basket with oil.
Place the fish in your air fryer basket and cook, flipping halfway, at 200 degrees C for 18 minutes.
While the fish is air-frying, prepare the sauce. In a medium-sized bowl, add the chili sauce, tomato ketchup and oyster sauce. Set aside.
In a wok over medium-high heat, heat the oil.
Add the garlic, ginger and onions and cook, stirring, until fragrant.
Add the bell peppers and lemongrass and cook, stirring, about 30 seconds.
Next, add the cilantro roots, cilantro stems and tomatoes and cook, stirring, until slightly soft, 1 to 2 minutes.
Add the bowl of sauces. Rinse the bowl with the water, and add to the pan. Stir until combined.
Add the pineapples, chilies, Thai chili paste, fish sauce, salt, sugar, lime leaves and lime juice, and stir until combined. Adjust seasoning to taste.
When the fish is done, transfer to a serving platter and ladle the prepared sauce over the fish. Discard the cilantro roots, lemongrass and lime leaves for a cleaner presentation.
Sprinkle with the chopped cilantro leaves.
Serve with plain white rice.