03Drain the greens of excess marinade and cram them into the pocket; you can overstuff as long as you don't tear the tuna (the tuna won't shrink, nor will the greens expand). If the pocket opening is small, seal it with a toothpick; if it's more than an inch or two wide, use two skewers. Marinate the tuna in the remaining soy mixture until the grill is hot, or up to an hour at room temperature or several hours refrigerated.04Grill the tuna, turning once, a total of about 6 minutes an inch of thickness (if your steak is 1 1/2 inches thick, for example, turn it after about 4 minutes and cook 4 or 5 minutes more). Season with salt and pepper, cut into 1/2-inch-thick slices and serve.