Crumble the uncooked chorizo sausage into a large skillet.

Cook the chorizo over medium heat for 6-8 minutes, or until fully cooked.

Drain off any excess grease from the cooked chorizo.

In a large bowl, whisk together the eggs, milk, ground mustard, and cayenne pepper until well combined.

Add the frozen O'Brien potatoes, shredded Monterey Jack cheese, corn and black bean salsa, and the cooked chorizo to the egg mixture.

Stir all ingredients together until evenly distributed.

Transfer the mixture to a greased 9 x 13 inch baking dish.

Cover the baking dish with a lid or aluminum foil and refrigerate overnight.

Remove the casserole from the refrigerator 30 minutes before baking.

Preheat oven to 350°F (175°C).

Bake the casserole uncovered for 55-65 minutes, or until a knife inserted near the center comes out clean.

Let the casserole stand for 10 minutes before cutting and serving.