Season fish on both sides with salt and pepper. In a small bowl, combine paprika, cayenne, garlic powder and cumin. Sprinkle over fish on both sides. Heat 1 tbsp oil in a grill pan on medium-high heat. Add half of the fish and cook until the edges are opaque, about 3 minutes. Flip and cook until fish flakes easily with fork, and is just ever-so-slightly translucent (it will finish cooking with the residual heat). Transfer fish to a plate and repeat with remaining fish.
To make cabbage slaw, toss all ingredients together in a large bowl.
To make crema, whisk all ingredients together and season to taste with salt.
Serve fish in warmed tortillas with cabbage slaw and a drizzle of crema.