COOK sausage in large nonstick skillet on medium-high heat 5 min.; drain. Add hash browns; cook 5 min. Cool 10 min.
HEAT oven to 350ºF. Add 1/2 cup cheese to hash brown mixture; mix lightly. Spoon down centers of tortillas; roll up. Place, seam sides down, in 10x6-inch baking dish sprayed with cooking spray.
WHISK eggs, milk and flour until blended; pour over enchiladas. Cover.
BAKE 30 min. Sprinkle with remaining cheese; bake, uncovered, 10 min. or until melted. Sprinkle with onions.