In large skillet, cook sausage over medium-high heat, stirring frequently until thoroughly cooked and no longer pink.
In large bowl, whisk together eggs, milk, and salt until thoroughly combined.
Evenly distribute half the bread into the prepared casserole dish. Sprinkle with half the cheese, half the black pepper, half the red pepper, and half the sausage. Repeat layers.
Pour egg mixture evenly over casserole.
Cover and refrigerate overnight.
When you're ready to bake the casserole, preheat oven to 325 F. Bake uncovered for 55-60 minutes, or until eggs are set. If the top begins to brown too quickly, loosely cover the casserole dish with foil.
Sprinkle the casserole with sliced green onions. Serve warm.