In a medium skillet, brown the sausage until no longer pink. Set aside.
Preheat a large cast iron skillet over medium heat. Add the potatoes and cook for 3 minutes. Add the onion, season with salt and pepper, and cook until the potatoes and onions are al dente, about 10 minutes. Add the mushrooms and cook for 5 minutes. Add the peppers and cook until everything is tender, about 10 minutes.
Stir in the breakfast sausage. Season to taste with salt and pepper.
Serve immediately with lots of butter. Store any leftovers in the refrigerator.
Sometimes I add spinach to the mix as well. I didn't have any on hand, so it was left out. If you have another favorite ingredient that you like in your hash, by all means throw it in!