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 tuna for about a minute and a half on each side. Remove the tuna and keep warm.
Reduce the heat. Add the reserved marinade to the skillet and bring to a boil. Reduce it until it becomes noticeably thicker.
Place the vegetables on the plate with the tuna on top, and nap with the reduced sauce. Garnish with satsuma sections or slices of orange.