Heat the cooking oil.
Rinse the fish. Pat dry with a kitchen towel. Sprinkle with salt. Dredge in starch.
Fry until a light crisp golden crust forms. Scoop out and set aside. Keep warm.
With a mortar and pestle (or a blender or food processor), process the garlic, shallots (or onion), lemongrass and chilies to a paste.
Pour off the cooking oil from the pan leaving only about two tablespoonfuls.
Reheat the cooking oil. Over medium heat, gently cook the paste with the fish sauce, sugar and tamarind paste until separate from the oil. It’ll take about ten minutes with occasional stirring.
Add the bell pepper strips, cook for another 30 seconds, taste, adjust the seasonings if needed.
Pour the sauce over the fried fish. Garnish with torn greens and serve with rice.