For a delicious and healthy meal, try marinating tuna steaks in soy sauce. The soy sauce adds a savory and slightly sweet flavor to the tuna, while also helping to tenderize the meat. Simply marinate the tuna steaks in a mixture of soy sauce, sesame oil, garlic, and ginger for at least 30 minutes, then grill or sear them to your desired level of doneness. Serve with steamed vegetables and rice for a complete meal.