½ cup soy sauce
2/3 cup fresh lime juice
3 tbsp. extra virgin olive oil
2 garlic cloves, finely minced
2 tbsp. minced or grated ginger
2 tbsp. light brown sugar
1½ lbs. fresh tuna fillets (1 inch thick)
2 small cucumbers, peeled
1 carrot, peeled and sliced very thin or grated (¼ cup)
1 tsp. finely chopped red jalapeño chile pepper or ¼ tsp. red pepper flakes
1 scallion, finely chopped (¼ cup)
1 tsp. sesame seeds
1 head green leaf lettuce, sliced into fine ribbons ¼ -inch thick (6 cups)
¼ cup loosely packed cilantro leaves
¼ cup loosely packed Thai or regular basil leaves
In a medium bowl, combine the soy sauce, lime juice, olive oil, garlic, ginger, and brown sugar (makes 1½ cups). Stir well. Pour half the mixture into a shallow dish large enough to fit the fish. Add the fish and marinate at room temperature 30 minutes or in the refrigerator 45 minutes. If refrigerating, remove the fish from the refrigerator 15 minutes before grilling.
Meanwhile, cut the cucumbers in half lengthwise. using a spoon, scoop out the seeds. Cut the cucumbers into ¼-inch thick slices crosswise (makes about 2 cups). Add the cucumbers, carrot, chile pepeper, scallion, and sesame seeds to the remaining marinade, and refrigerate until ready to serve.
Remove the fish to paper towels and discard the marinade in the dish. Pat the excess marinade from the tuna. With a pastry or barbecue brush, brush the fish with additional olive oil.
On an outdoor grill or a grill pan over high heat, lightly brush the grates with olive oil (do not place the fish on the grill until the flames have subsided). Grill the fish 3 to 5 minutes on both sides for medium rare or 6 to 8 minutes for medium well. When slightly cooled, cut into thick slices. Mean while, mix the lettuce and herbs with the chilled marinade and gransfer to a platter place the fish on top, and drizzled additional marinade over the fish. Serve immediately.