Preheat oven to 400 degrees F. Heat a 12 inch cast iron pan over medium heat.
Add pancetta and cook for 3-5 minutes, until fat is rendered and meat is starting to crisp up.
Add garlic and onion, and cook for about 2 minutes until onion is starting to become translucent. Add mushrooms and Brussels sprouts and cook an additional 5 minutes.
Make four shallow wells in the hash. Crack one raw egg into each well.
Bake for 5-10 minutes or until whites are set. A shorter amount of time will yield a runny yolk, while 10-11 minutes will yield a fully hardened yolk.