Grease a round pie dish with butter or oil. Lay one torilla in the base, add the cooked chicken, place another tortilla on top and cover with the beans, cream, salsa, chicken and guacamole. Place the final tortilla over this. (If you only have two just make a big sandwich).
Beat the eggs and milk together in a bowl, season and pour over the tortilla layers.
Cover with foil and leave to rest in the fridge for 2-3 hours to let the egg mix soak in.
Heat the oven to 180 C
Grate the the cheese over the top of the tortillas.
Replace the foil and bake for 20 minutes until the egg is almost set.
Increase the oven temperature to 220 C
Remove the foil and bake for a further 5-10 minutes until the cheese is browned and melted.
Serve cut into wedges with salad or vegetables.