In a skillet sprayed with nonstick cooking spray and heated to medium, add onion and saute until translucent. Add chicken sausage, giving everything a slight sear. Add mushrooms, sliced apple, and chopped sage, continually stirring.
When apples and mushrooms are soft & slightly browned, pour everything into a 9x13 inch pan sprayed with nonstick spray.
Whisk together (really well!) eggs and egg whites; whisk in cottage cheese. Pour over sausage-mushroom-apple mixture.
Bake at 350 degrees F for 30 minutes, until eggs are set (basically when they no longer move when you shake the pan).
Remove from oven and grate cheddar over top. It will instantly melt! We like to sprinkle on a little more fresh sage, too. Serve!