Preparation Place tuna in shallow glass dish. Pour marinade over and turn to coat. Let tuna stand 10 minutes at room temperature, or cover and refrigerate 1 hour. Mix butter, wasabi powder, and chives in small bowl. Prepare barbecue (medium heat). Remove tuna from marinade; brush on both sides with oil. Sprinkle with salt and pepper. Grill fish, brushing occasionally with remaining marinade, about 2 minutes per side for medium-rare. Transfer to platter. Top with wasabi butter and serve.
Preparation Place tuna in shallow glass dish. Pour marinade over and turn to coat. Let tuna stand 10 minutes at room temperature, or cover and refrigerate 1 hour. Mix butter, wasabi powder, and chives in small bowl. Prepare barbecue (medium heat). Remove tuna from marinade; brush on both sides with oil. Sprinkle with salt and pepper. Grill fish, brushing occasionally with remaining marinade, about 2 minutes per side for medium-rare. Transfer to platter. Top with wasabi butter and serve.