This is a receipe for fresh tuna Hawaiian Style.

Marinade:
Soysauce
Green onions
Garlic (Fresh)
Ginger (Fresh)
Sesame oil
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1 cup of Soy sauce
1/3 cup water
1 tp. sesame oil
3 cloves of garlic choped/minced
small root of Ginger cut in slices(only fresh, no powder)
2 green onions chopped
Mix all ingridents in a bowl
Add the tuna steaks and marinade for 2 hours.
If on the grill, sear the outside (depending on the thickness, 2 min each side) do not over cook. Middle should be translucent.