Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add sausage to pan; cook 5 minutes or until browned, stirring well to crumble.
Arrange bread in a 13 x 9-inch baking dish coated with cooking spray. Top evenly with cooked turkey sausage and cheddar cheese. Combine 2 1/2 cups milk, egg substitute, and Dijon mustard, stirring with a whisk. Pour over bread mixture in dish. Cover and refrigerate 8 hours or overnight.
Preheat oven to 350°.
Uncover casserole. Combine remaining 1/2 cup milk and cream of mushroom soup, stirring with a whisk. Pour over bread mixture. Bake at 350° for 1 hour and 5 minutes or until set and lightly browned. Let stand 15 minutes before serving.