Over medium heat, heat a large nonstick skillet. Cook, tossing to break up any large chunks, until the turkey is browned and cooked through, about 10 minutes. Remove from the heat and set aside to cool.
In a large mixing bowl, whisk together the eggs, egg whites, milk, and 1/2 teaspoon salt and pepper. Toss together the cooked sausage, spinach, cheeses, and bread to properly distribute the ingredients.
Using cooking spray, coat a 3-quart casserole dish. In the dish, evenly distribute the egg mixture. Refrigerate for at least 6 hours, ideally overnight, after covering.
Preheat the oven to 350 degrees Fahrenheit. Bake for 30 minutes, uncovered until the casserole is set and lightly browned on top.