Makes: 4 sandwiches at $3.81 each. Prep: 10 minutes. Refrigerate: 15 minutes. Grill: 6 minutes.
1. Whisk soy, oil, juice and ginger in bowl. Pour over tuna in baking dish. Refrigerate 15 minutes, turning once. Mix mayonnaise, ginger, soy in bowl. Refrigerate.
2. Prepare grill with medium-hot coals; coat rack with cooking spray. Or coat stove-top grill pan; heat over high heat until pan starts to smoke slightly, about 3 minutes.
3. Remove tuna from marinade; pat dry with paper toweling. Cook on grill or pan, 3 minutes a side for medium. Transfer to platter; tent with foil.
4. Spread bread with mayonnaise; make 4 sandwiches with lettuce, avocado and tuna.