Prepare Citrus Vinaigrette. Place tuna in a nonmetal dish; drizzle with 1 cup Citrus Vinaigrette. Cover and marinate in vinaigrette in refrigerator 1 hour, turning tuna once. Drain, reserving vinaigrette marinade. Place vinaigrette marinade in a small saucepan; bring to a boil. Remove from heat; set aside.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Place tuna on rack; grill, covered, 5 minutes on each side or until fish flakes easily when tested with a fork, basting often with reserved marinade. Discard skin from tuna. Cut tuna into bite-size pieces, and set aside.
Combine Boston lettuce and remaining 8 ingredients in a large bowl. Drizzle with remaining 3/4 cup Citrus Vinaigrette; toss well. Add tuna, and toss gently.
