Preheat oven to 350 degrees F. Spray a 13" x 9" pan with cooking spray.
In a large skillet oven medium-high heat, add olive oil, then onions and bell peppers. Cook, stirring often, for about 3 minutes. Add sausage and continue to cook and stir for another 3-4 minutes, or until vegetables are soft. Set aside.
In a large bowl, whisk together eggs, milk, salt and pepper until well combined.
Layer thawed shredded potatoes in the bottom of the pan. (*tip - to thaw quickly, spread out on a cookie sheet and place in the oven while it heats and while you prepare the rest of the ingredients). Top with sausage and pepper mixture, then cheese, then eggs. Use a fork or spoon to stir ingredients together slightly to make sure that the eggs are evenly distributed.
Bake in the 350 degree oven for 1 hour. Let cool for 10 minutes before serving.
Can be stored in the refrigerator for 3-4 days in a tightly sealed container, or in the freezer for up to 2 months.
*Tip - Prepare casserole and slice into individual portions. Arrange on a cookie sheet, not touching, and freeze. Once frozen place in a sealed freezer bag. Pull out individual portions, wrap in a wet paper towel and heat in the microwave for 2-3 minutes, or until hot.