Combine the grapes, cucumber, pickled ginger, lime juice, mirin and salt. Chill while preparing the fish to blend flavors.

Heat the oil in a large skillet over medium high heat. Pan fry the mackerel until the skin is crisp and the meat is firm, about 3 to 4 minutes on each side.* Lightly salt to taste. Serve immediately with the grape relish and a garnish of spicy daikon sprouts.

*Alternate methods: broil or grill the fish over a medium high heat, with the skin facing the heat source, until it is cooked through and the skin is crisp, 7 to 8 minutes.