Cook the sausage in a saute pan over medium heat for 3 minutes, breaking it into bite size pieces. (If using fully cooked sausage, add some olive oil to the pan and heat through.)
Add the mushrooms, bell peppers, 1 tsp of salt and pepper. Continue to cook for 5 minutes. Let cool.
Preheat oven to 375 degrees.
In a bowl, beat the eggs, 1 tsp salt and milk. Add the cheese and stir to combine.
Butter the 13×9 inch baking dish and add the bread cubes and cooled sausage mixture. Toss to combine.
Pour the egg mixture over the bread and sausage, pressing the bread mixture down gently to soak up some of the egg mixture.
Cover the dish with foil and bake for 30 minutes.
Uncover the dish and continue to bake an additional 20 minutes.