There are so many ways of cooking Tuna steaks. The key is not to overcook this fish and to find a comfortable for you doneness. Some people are comfortable with red or pink center. For my family, we tend to like our steaks on Medium-Well side. So please cook according to your taste.
Marinate the Tuna steaks first and let sit at room temperature for 30 minutes to absorb the flavors. I have tried many Teriyaki sauces, but I love this Veri Veri Teriyaki Low-Sodium the most. Thick with lots of taste. For the marinade, I use: about 3 to 4 tablespoons of Teriyaki sauce, a tablespoon of honey, tablespoon of freshly squeezed lemon and a tablespoon of Garlic powder.
I use the same method for both fish and meat. Preheat the skillet to Medium-Hot. Add oil and sear fish for 2 -3 minutes on each side to create a nice browned crust. This will seal in the moisture. If you are ok with pink in the middle, you are done. If not, cover the skillet with a lid and let it cook on the inside for another couple of minutes.
Transfer the Tuna steaks to warm plate and saute your veggies in a leftover marinade.
Fancy and Delicious meal! Enjoy!
FYI: The label sushi/sashimi grade means that it is the highest quality fish the store is offering, and the one they feel confident can be eaten raw. Tuna, for example, is inspected and then graded by the wholesalers. The best ones are assigned Grade 1, which is usually what will be sold as sushi grade.