Preheat the oven to 350 degrees F and spray a baking sheet with oil.

Place the quartered tortillas on the baking sheet and lightly spray with the oil.

Bake for 5 minutes and then set aside.

In a large bowl, whisk the egg. Add the milk, sour cream, salsa, chicken, cream cheese, cilantro, scallions and salt. Stir to combine.

Spray a 7x11 baking dish with oil. Arrange half of the tortillas in the dish. Spread half of the chicken mixture on top of the tortillas, then sprinkle half of the cheese on top. Repeat this for a second layer.

Bake, uncovered, for 35 minutes, or until the casserole is bubbling and the cheese is golden brown.