Empty Pasta mix into 3-quart saucepan 2/3 full of boiling water. Gently boil uncovered 12 minutes, stirring occasionally, adding corn during last 2 minutes of cooking.
Drain pasta and corn; rinse with cold water. Shake to drain well.
In large bowl, stir together Seasoning mix, mayonnaise and barbecue sauce. Stir in pasta, corn, chicken and tomatoes. Line serving plate with lettuce leaves. Top with salad mixture; sprinkle with green onions. Serve immediately, or cover and refrigerate 1 hour to chill.