1 cup teriyaki sauce
1/2 cup dry sherry
4 tablespoons finely chopped fresh ginger
1/2 cup chopped scallions
2 cloves garlic, thinly sliced
1/2 teaspoon cayenne pepper
2 teaspoons freshly ground black pepper
2 lemons, juiced
4 (8 to 10-ounce) yellowfin tuna steaks, cut into 3-inch cubes
2 tablespoons olive oil
1/4 cup Japanese pickled ginger (available at Asian markets)