For wasabi mustard sauce: In a small bowl, combine vinegar and wasabi; stirring until blended. Stir in soy sauce, lime juice and mustard until blended.
Prepare a hot fire for direct grilling. Spray or rub clean grill with oil.
In a separate small bowl, combine paprika, garlic powder, onion powder, lemon pepper, cayenne pepper, five-spice powder and salt; mix well. Sprinkle spice mixture over entire tuna.
Place tuna on hot fire, searing on both sides until 1/4" of outside of fish is cooked.
Remove fish and cut into 1/4" slices. Arrange slices over a serving plate of shredded carrots and garnish with pickled ginger. Spoon a little wasabi mustard sauce over tuna slices. Serve with remaining sauce on the side.
For best results, select a sashimi-grade tuna 1-2" thick. The key to this recipe is to sear the tuna over a very hot fire, cooking only 1/4" of the outside of the fish. The inside should be raw.