1. Combine the paprika, cumin, cayenne, sugar, and 3/4 teaspoon of salt on a sheet of wax paper. Dredge the tuna steaks in the mixture until each is well coated.
2. Heat the oil in a ridged grill pan or large nonstick skillet over high heat. Add the tuna steaks and cook until the steaks are seared and cooked to the desired doneness, about 2 minutes on each side for medium.
3. Meanwhile, combine the peppers, half-and-half, garlic, and remaining 1/4 teaspoon salt in a blender and puree. Transfer to a microwavable bowl and microwave on High, stirring twice, until bubbling, about 1-1 1/2 minutes.