Heat a tiny bit of olive oil in a frying pan on medium-high heat.
Put tortilla on pan. It should sizzle just a bit. If it sizzles like crazy, the pan is too hot. If it doesn't sizzle, everything will still be fine, but you won't get a good crunchy outside.
Quickly put shredded cheese and chicken on the tortilla.
If you want any other ingredients in your quesadilla, add them now.
When you see the first indications that the cheese is melting, fold the tortilla in half and press down so the sides stick to each other properly.
Flip back and forth a few times until the outer shell starts to get a bit of a crunch. Be careful: if you let it cook too long, it will burn.