1. Heat oven to 375º F.
2. Place vegetables in a colander in the sink. Cook macaroni as directed on the package, then pour over vegetables to drain macaroni and thaw vegetables. Return to saucepan.
3. Stir in cheese sauce, milk and dressing. Add tuna and a 1/2 cup cheddar, and mix well. Spoon the mixture into a 2-qt. casserole dish, then cover.
4. Bake for 35 minutes or until heated through. Top with the remaining cheddar and bake for 3 to 4 minutes or until melted.