Preheat a comal for 1 minute over medium-low heat. The temperature on the skillet is important so that the tortillas do not harden or overcook before the cheese fully melts.
Warm tortillas for 1 minute on one side, flip and sprinkle some of the cheese on one of the tortillas, add chile, and top with another tortilla and press gently with a spatula.
Flip occasionally until quesadillas are golden brown on each side and cheese has melted.
Repeat with remaining tortillas and ingredients.
Top them with salsa and guacamole, if desired.
Notes
Choose chile according to your tolerance for heat. For a very mild flavor roast poblano chile peppers or for a shortcut try canned Hatch diced green chile.
If you are unsure how to roast chile peppers, please refer to this blog post: How to roast chile peppers.