Recipe: Sausage and Greens Breakfast Casserole

Name: Recipe: Sausage and Greens Breakfast Casserole
Ingredients: 1 pound frozen diced potatoes (about 4 cups, do not thaw); 1 tablespoon olive oil, plus more for the baking dish; 1 pound uncooked breakfast sausage, casings removed; 1 medium yellow onion, diced; 1 1/2 teaspoons dried oregano; 5 ounces baby spinach (about 5 packed cups); 8 large eggs; 1 1/2 cups whole or 2% milk; 1 1/2 teaspoons kosher salt; 1/4 teaspoon freshly ground black pepper; 2 cups shredded Italian blend cheese (such as Parmesan, mozzarella, provolone)