Cook bacon in large skillet on medium heat 10 min. or until crisp. Remove bacon from skillet with slotted spoon; drain on paper towels. Discard all but 2 Tbsp. drippings from skillet.
Add potatoes, mushrooms, peppers and onions to reserved drippings in skillet; cook 10 min. or until peppers and onions are crisp-tender, stirring occasionally. Stir in VELVEETA. Spoon into 13×9-inch baking dish sprayed with cooking spray.
Whisk eggs and sour cream in medium bowl until blended; stir in bacon. Pour over vegetable mixture.
Bake 40 min. or until center is set and casserole is heated through.