Heat oil: Pour 2 liters vegetable oil for frying into a heavy pot or dutch oven to a depth of 3 inches. Heat to 375F. Use a thermometer — temperature control is the whole game here.
Make the dredge: Whisk together 0.8 cups all-purpose flour, 1 teaspoons ground cumin, 1 teaspoons ground coriander, 1 teaspoons smoked paprika, 0.5 teaspoons dried thyme, 0.5 teaspoons garlic powder, 0.3 teaspoons cayenne, 1 teaspoons kosher salt, and 0.5 teaspoons black pepper in a shallow bowl.
Prep the fish: Pat cod pieces completely dry with paper towels. Moisture is the enemy of crust. Season the fish lightly with salt before dredging.
Dredge: Press each piece firmly into the spiced flour on all sides. Shake off excess — you want a thin, even coat, not clumps.
Fry: Fry in batches of 2-3 pieces, 3-4 minutes depending on thickness, turning once. Oil should bubble actively but not violently. Internal temp 145F.
Drain and serve: Transfer to a wire rack over a sheet pan — not paper towels, which steam the crust soft. Hit immediately with a pinch of salt and serve with 2 lemon, cut into wedges.