Cook pasta according to package directions. Drain; cool.
Mix pasta with tomatoes, sweet peppers and carrot in large bowl.
Mix together lemon juice, olive oil, sugar, salt, celery seeds and pepper in small bowl. Whisk in mayonnaise until smooth.
Fold ham, cheese and mayonnaise dressing into pasta and vegetables until evenly coated.
Refrigerate, covered, at least 3 hours, preferably overnight. Can be prepared up to 2 days ahead. Makes 18 servings.