Place 6 of the bread slices on bottom of greased 13x9-inch baking dish; top with bacon, mushrooms, onions and VELVEETA Made With 2% Milk. Cover with remaining 6 bread slices.
Beat eggs and milk with wire whisk in large bowl until well blended; pour over bread. Cover and refrigerate at least 1 hour or up to 24 hours.
Preheat oven to 350F.
Bake casserole, uncovered, 50 min. to 1 hour or until knife inserted in center comes out clean.