HEAT oven to 350°F. 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 13x9-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. Kraft Kitchens Tips: Size Wise Looking for something to serve as part of your next brunch menu? This satisfying casserole is sure to fit the bill since it makes enough for 12 servings. Make Ahead: Casserole can be assembled ahead of time. Refrigerate up to 24 hours before baking as directed, increasing the baking time if needed until casserole is done. Substitute: Substitute 1 pkg. (8 oz.) KRAFT Shredded Cheddar Cheese for the cubed VELVEETA.