In A Bowl, Combine Soup And Milk Until Smooth. Add The Tuna, Macaroni, Peas, Onions And 3/4 Cup Cheese; Mix Well. Pour Into A Greased 2-Qt. Microwave-Safe Dish. Cover And Refrigerate Overnight. Microwave, Covered, On High For 15-17 Minutes Or Until Bubbly. Uncover; Sprinkle With Remaining Cheese And Let Stand For 5 Minutes Or Until Melted.