1Heat gas or charcoal grill. In small bowl, mix all dressing ingredients with wire whisk; reserve 2 tablespoons.
2On each of 2 (10-inch) metal skewers, thread pineapple, leaving 1/4-inch space between each piece. Brush 1 tablespoon of the reserved dressing on pineapple; brush remaining 1 tablespoon reserved dressing on tuna.
3Carefully spray grill rack with cooking spray. Place tuna on grill. Cover grill; cook over medium heat about 10 minutes, turning once and adding pineapple for last 5 minutes of grilling, until fish flakes easily with fork and is slightly pink in center.
4Among 4 plates, divide salad greens, tomatoes and onion. Top each with pineapple and tuna. Sprinkle with sesame sticks. Serve with remaining dressing.