PLACE vegetables in colander in sink. Cook Macaroni as directed on package; pour over vegetables. Drain well; return to saucepan.
STIR in Cheese Sauce Mix, milk and dressing. Add tuna and 1/2 cup shredded cheese; mix well. Spoon into 2.3-L casserole dish; cover.
BAKE 35 min. or until heated through. Top with remaining shredded cheese; bake 3 to 4 min. or until melted.
Assemble casserole as directed. Refrigerate up to 24 hours. When ready to serve, bake, covered, at 375°F for 40 to 45 min. or until heated through. Top with remaining shredded cheese; continue as directed.
Substitute 1 lb. extra-lean ground beef, cooked and drained, for the tuna.