Use a pastry cutter roughly 4 inches in diameter, (or cut around a large glass with a knife), to cut out 4 circles from each tortilla. Cut out one circle of the same size from each slice of cheese.
Take 4 of the tortilla circles and top each with a slice of cheese, slices of red onion and avocado, a spoonful of salsa and a sprinkle of coriander.
Heat up a large frying pan and place the quesadillas in carefully. Cook for 1-2 minutes until starting to turn golden brown on the bottom, then flip over and cook for a further minute on the other side.