Position rack in center of oven. Preheat to 325*. Coat non-stick muffin tin generously with cooking spray.

Heat large non-stick skillet over medium heat. Add sausage and cook until golden brown, 6-8 minutes. Transfer to bowl to cool. Add oil to pan. Add mushrooms and cook, stirring often, until golden brown, 5-7 minutes. Transfer mushrooms to the bowl with the sausage. Let cool for 5 minutes. Stir in scallions, cheese, and pepper.

Whisk eggs, egg whites and milk into medium bowl. Divide egg mixture evenly into prepared muffin cups. Sprinkle a heaping tablespoon of sausage mixture into each cup.

Bake until tops are just beginning to brown, 25 minutes. Let cool on wire rack for 5 minutes. Place rack on top of the pan, flip it over and turn quiches out onto the rack. Flip upright and let cool down.