Heat oil in a large saute pan over medium-high heat. Add potatoes and onion and cook until potatoes are slightly brown and onions are translucent, 12 to 15 minutes.

Heat a small saute pan over medium-high heat. Saute sausage, apple, cranberries, salt, black pepper, fennel, rosemary, and red pepper flakes for 5 minutes. Add to potato mixture and serve.