Substitute 1 lb. extra-lean ground beef, cooked and drained, for the tuna.
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 cheese; continue as directed.
Prepare using 2 (5-oz.) cans tuna.