1. In large skillet, cook sausage and onion over medium heat until no longer pink; drain.
2. Place bread cubes in a greased 13 inch baking pan.
3. Layer with sausage mixture, red peppers, brie and Parmesan cheese, and basil.
4. In large bowl, whisk eggs, cream, mustard, pepper, and salt; pour over top.
5. Cover and refrigerate overnight
6. Remove from the refrigerator 30 minutes before baking.
7. Bake uncovered at 350° for 45 to 50 minutes or until a knife inserted comes out clean.
8. Sprinkle with mozzarella cheese.
9. Bake 4 to 6 minutes longer or until cheese is melted.
10. Let stand for 10 minutes before cutting.
11. Sprinkle with green onions.