In a bowl mix together the soy sauce, sesame oil, brown sugar, minced garlic, and ginger. Set to the side.
Rinse and pat dry the tuna steaks. Season with salt and pepper to taste on both side.
Heat a skillet to high heat with the grape seed oil. Place tuna steak in skillet (you should hear a searing sound). Cook 2 minutes, then flip.
Spoon half the sauce into the pan during the last minute of cooking.
Remove the tuna steaks and slice thin (or keep whole).
Pour half the remaining sauce over the tuna steaks, and sprinkle with sesame seeds, dividing evenly. Enjoy.
When searing tuna you want it the fish to be very dry with now water present on the fish.
I like to use a cast iron frying pan and get it extremely hot. When the fish goes on the oiled pan it should start smoking and spraying oil everywhere. That's how you know you are cooking this fish right.
Find the sharpest knife you have to cut tuna against the grain.
To make this recipe gluten free use Tamari which is a gluten free soy sauce.