3 tablespoons soy sauce
1 teaspoon sugar
1/8 teaspoon dried red pepper flakes
1/2 cup canned low-sodium chicken broth or homemade stock
4 tuna steaks, about 1-inch thick (about 2 pounds in all)
1/2 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
2 tablespoons cooking oil
1 teaspoon sesame oil
1 scallion including green top, chopped
3 garlic cloves, minced
In a small bowl, combine soy sauce, sugar, red pepper flakes, and broth. Sprinkle fish with salt and black pepper. Heat cooking oil in a large frying pan over moderately high heat. Add tuna and cook until brown, about 3 minutes. Turn and cook fish until done to your taste, 3 to 4 minutes longer for medium rare. Transfer tuna to a cutting board to rest while you make the sauce.
Reduce heat to moderately low and add sesame oil to pan. Stir in scallions and garlic and cook, stirring, until fragrant; about 1 minute. Add soy sauce mixture to pan and simmer until reduced to approximately 1/3 cup, about 2 minutes. Cut tuna into slices and serve with sauce.