Preheat oven to 375 degrees F. Cook the potato dices in salted boiling water for about 5 minutes. Drain and let cool.

Remove casings from sausage, unless you are making your own mix. Heat a large skillet to medium-high and cook the sausage until browned. Break it up in the process. Remove from skillet with a slotted spoon, leaving 1 tablespoon of grease.

Cook the onion and red pepper in the sausage grease for about 5 minutes. Add the garlic and cook a couple more minutes. Fill into a large baking dish together with sausage and potato dices.

In a large bowl, whisk together the eggs, milk and black pepper. Add 1.5 cups of the shredded cheese and stir to combine everything. Pour into the baking dish.

Sprinkle the remaining cheese on top, cover with foil and bake for 20 minutes. Uncover and continue baking for 10-15 more minutes.

Let the breakfast casserole rest for a few minutes. Add sliced green onion and serve hot.