Preheat oven to 325F. Coat a skillet with nonstick cooking spray and cook sausage over medium-high heat for 10 minutes or until no longer pink. Drain and set aside. Add oil to skillet, heat to medium-high and add onion and mushrooms. Saute until onion is tender, about 5 minutes. Add the spinach, tomatoes and garlic. Cook 2 minutes or until spinach is wilted. Add the sausage and sun dried tomatoes. Mix well. Lightly grease a 13x9 inch baking dish with cooking spray. Layer the bread cubes, cheese, sausage mixture, repeating layers. In a medium bowl, whisk together the milk, eggs, pepper, salt until well blended. Pour egg mixture over the layers. Bake for 1 hour or until set and lightly browned. Let stand 10 minutes and then serve.