Cheese in Latin America is often nothing to write home about. Quesillo is the exception to this rule. A soft, white, stringy cheese usually rolled up into a ball, Quesillo has a mild flavor, similar to mozzarella. It is hard to find anywhere outside of Oaxaca, so after a taste, you will understand why so many people insist on eating as much of it as possible while in the area.
Probably the most Oaxacan thing to eat Quesillo on, is a Tlayuda, which is best described as a Mexican Pizza. It is a big crunchy tortilla, covered in beans, lettuce, meat, salsa, and Quesillo. A vendor selling Tlayudas can be found at nearly ever corner in Oaxaca. They are in particular a delicious midnight snack, but really can be enjoyed any time of the day.