Start by cooking the breakfast sausage in a pan. When fully cooked, remove then sauté the bell peppers and onions. You can add them in raw but there's far more flavor if you cook them first.
Add all of the cooked ingredients into the crockpot. Now, in a bowl add the eggs, sour cream, salt and pepper then use a hand mixer until the eggs are beaten and everything is smooth.
Pour the beaten eggs in the crockpot along with the shredded cheese, then fold everything together.
Turn the crockpot on low for 6-8 hours or overnight and the casserole will be ready in the morning.