Place the chopped bell peppers, red onion, eggplant, and asparagus on one large, or two medium, sheet pans, then drop bite-sized pieces of the breakfast sausage on top of the vegetables and bake for 45 minutes, until caramelized.
In a large bowl, whisk together eggs, salt, and pepper.
Add vegetables and sausage to a deep 9×13 inch baking dish. Pour the eggs over the vegetables, then sprinkle on bagel spice blend.
Bake the casserole for 30-35 minutes or until the center is firm (give it a shake and if it jiggles, it needs more time).
Let the casserole cool for 5-10 minutes, then cut and serve!