Ingredients

1. 1/2 cup plus 1/2 teaspoon soy sauce
2. 1/4 cup sake
3. 1/4 cup sugar
4. 4 scallions, thinly sliced
5. 2 garlic cloves, minced
6. Four 6-ounce sushi-quality tuna steaks, about 1 inch thick
7. Vegetable oil
8. 1 tablespoon fresh lime juice
9. 1 tablespoon mirin or sweet sherry
10. Salt and freshly ground pepper
11. 2 carrots, cut into thin matchsticks
12. 1 European cucumber--peeled, seeded and cut into thin matchsticks
13. 1 package (2 ounces) radish sprouts
14. 1/2 Maui or other sweet onion, sliced paper thin 

Directions

1. 1. In a glass baking dish, combine 1/2 cup of the soy sauce with the sake, sugar, scallions and garlic; stir to dissolve the sugar. Add the tuna steaks and turn to coat. Marinate in the refrigerator, turning occasionally, for 1 hour.
2. 2. Light a grill. Lightly brush the grate with vegetable oil. Remove the tuna from the marinade and pat dry. Brush the tuna with 1 tablespoon of vegetable oil and grill over high heat until lightly browned, about 2 to 3 minutes per side for medium rare. Transfer the tuna to a plate, cover loosely with foil and keep warm.
3. 3. In a medium bowl, whisk 1 tablespoon of vegetable oil and 1/2 teaspoon of soy sauce with the lime juice and mirin. Season with salt and pepper. Add the carrots, cucumber, radish sprouts and onion and toss to combine. Mound the slaw on 4 dinner plates. Thickly slice the tuna and arrange it over the slaw. Pour any accumulated juices over the tuna and serve.

Make Ahead

The marinade can be refrigerated in an airtight container for up to 2 days.