Combine all of the marinade ingredients and whisk vigorously.
Place tuna steaks in a gallon ziploc bag. Add the marinade, toss to coat the tuna steaks, press out excess air and seal (if using ziploc bag)
Transfer to the fridge and chill for 30 minutes.
Grill 6-8 minutes on each side until easily flaked with a fork and center of tuna steak is just barely pink. Internal temperature should read 90-95 degrees when done. Alternately, steaks can be seared in a skillet over medium-high heat, or broiled in the oven at 400 degrees.
