Dice the potatoes. Fry them in oil over medium heat until they get annoyingly hard to stir due to sticking to the pan. Add salsa, stir to mix, turn down heat, and cover. You may need to add a little water to reduce sticking.
When the potatoes are cooked through, remove the cover and top with cheese. Keep over the heat until the cheese melts.
If you add enough leftover meat, this can become a heartier dish suitable for dinner.