Preheat oven to 350°. Whisk together eggs, milk, salt and pepper. In a large skillet coated with cooking spray, cook and stir egg mixture over medium heat until thickened and no liquid egg remains; remove. , In the same skillet, cook and crumble sausage over medium heat until no longer pink, 5-7 minutes; drain. Stir together sour cream and soup. Spread half the sour cream mixture in an ungreased 13x9-in. baking dish. Layer with half the tortilla pieces, half the salsa, the scrambled eggs, the sausage, and the remaining tortillas and sour cream mixture. Top with remaining salsa; sprinkle with cheeses., Bake, uncovered, until heated through, 30-35 minutes. If desired, serve with enchilada sauce and sliced green onions., To Make Ahead: Refrigerate unbaked casserole, covered, several hours or overnight. To use, preheat oven to 350°. Remove casserole from refrigerator while oven heats. Bake as directed, increasing time by 5 minutes.