Step 1

Heat oil in a large skillet over medium. Cook bell pepper, shallot, garlic, chile, and ginger, stirring occasionally, until softened and golden brown in spots, 5–8 minutes. Transfer to a blender. Add vinegar, dried thyme, sugar, and 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt; purée until smooth. Season sauce with more vinegar and/or salt if needed. Transfer to a small bowl.

Step 2

Grind coriander, fennel, cumin, and fenugreek seeds in a spice mill or with a mortar and pestle to a fine powder (it won’t be as fine with mortar and pestle); transfer to a small bowl. Mix in garlic powder, paprika, sugar, turmeric, MSG (if using), and 4 tsp. Diamond Crystal or 2½ tsp. Morton kosher salt, then stir in vinegar to make a paste.

Step 3

Place fish on a cutting board; pat dry. Using a knife, make slashes crosswise every 2" along body of fish, cutting all the way down to the bones. Turn over and repeat on other side. Season fish all over with salt, including inside cavity and slashes. Rub spice paste over fish, tucking some into slashes. Pour rice flour onto a rimmed baking sheet. Coat fish evenly in rice flour, shaking off any excess.

Step 4

Heat oil in a large wok or cast-iron skillet over medium-high until an instant-read thermometer registers 365°. Grip a fish by the tail and carefully lower, head first, into wok, making sure to lay it down away from you and releasing gently. Fry until cooked through and skin is deeply browned and crisp, about 4 minutes per side (use tongs and a fish spatula to turn). Transfer to a wire rack. Repeat with second fish. Sprinkle lightly with salt.

Step 5

Serve fish with sauce and lime wedges.