Spread croutons in a lightly greased 9"x13" dish; set aside. Cook sausage until browned, stirring to crumble; drain well. Sprinkle sausage over croutons.
Combine eggs, milk, soup, mustard and mushrooms. Mix well and pour over sausage. Cover and refrigerate at least 8 hours or overnight
Remove from refrigerator; let stand 30 minutes. Bake uncovered at 325 degrees for 50-55 minutes. Sprinkle cheese on top and bake 5 minutes or until cheese is melted. Garnish with cherry tomatoes and parsley if you want to..