Brown the sausage in a frying pan over medium heat, breaking sausage up with a spoon, add scallions for the last 5 minutes. Remove from heat and let cool, about 10 minutes. Drain any excess fat.
Whisk the eggs, egg whites, milk and about ½ teaspoon each of salt and pepper in a large bowl until combined.
Add the cooked sausage, drained and squeezed spinach, cheeses and bread. Toss to distribute ingredients evenly.
Spray a 3 quart, shallow casserole with cooking spray. (I used a 9 X 13 casserole.) Spread the egg mixture evenly in the dish. Cover and refrigerate for at least 6 hours or overnight.
Preheat oven to 350 degrees F. Bake the casserole, uncovered until set and lightly browned on top, about 30 minutes.
Recipe by Baking Free at https://gfbakingfree.com/too-much-bread-here-what-shall-i-do/