In a medium sized bowl, combine all ingredients except the tuna to create a marinade.

Slice tuna steaks into 4 fillets and place into marinade. Cover and refrigerate for at least an hour.

Spray a large, nonstick skillet with non-fat cooking spray or an olive oil mister, and set over a medium high heat. Once the skillet is hot enough, sear the tuna steaks for a minute to a minute and a half on each side, or longer if you prefer them less rare.

Remove from pan and slice into 1/4-inch thick slices. Garnish with additional green onion slices.