Combine all the ingredients for the marinade in a wide shallow bowl. Marinate the tuna steaks for about a minute on each side, then wrap them (still dripping) with plastic wrap. Refrigerate for at least an hour. Save the remaining marinade.
To begin cooking, heat 2 Tbs. of the butter in a skillet and cook the cabbage, carrots, and green onion with the teaspoon of soy sauce until the vegetables wilt. Remove from the heat.
Heat a heavy skillet over medium-high heat with the remaining butter. Sprinkle the tuna with salt and pepper. Cook the wahoo for about a minute and a half on each side. Remove from the pan and keep warm.
Reduce the heat. Add the reserved marinade to the skillet and bring to a boil. Slightly reduce it.``
Place the vegetables on the plate with the fish on top, and nap with the reduced sauce.