In a large pan, over medium-high heat, add 1/2 of the oil, onion and garlic and sauté until translucent, about 3-5 minutes.

Add potato and cook until fork­ tender, about 15 minutes. Remove from the pan and add to a lightly greased baking dish about 12x8-inches.

Add the other 1/2 of the oil to the pan and sauté mushrooms until browned, about 2 minutes. Add to the baking dish as a second layer.

Using the same pan, add the sausage removed from the casing, and cook until browned, about 3-5 minutes. Add the browned sausage to the baking dish as a third layer. At this point, you can cover and refrigerate overnight if you want to wait to bake and serve.

When ready to bake, preheat the oven to 350ºF.

In a medium-sized bowl, whisk the eggs and pour over the casserole mixture in the baking dish.

Bake for 30-40 minutes, or until the eggs are no longer runny. Serve hot and garnish with a sprinkle of scallions.