Preheat the oven to 350 degrees F. Spray a 13x9 casserole dish with nonstick spray and set aside.
In a medium bowl, whisk together the Greek yogurt, skim milk, and salsa.
Add the chicken, corn, bell pepper, and half of the cheddar cheese and stir to combine.
Arrange 4 of the corn tortillas over the bottom of the casserole dish, overlapping if necessary.
Top the tortillas with 1/3 of the chicken mixture. Cover the chicken with 4 tortillas and repeat the process.
Sprinkle the remaining cheddar cheese on top of the final layer of tortillas and bake for 30 minutes, covered with aluminum foil, until the mixture is warm and bubbly.
Remove the foil and bake for an additional 10 minutes, until the cheese is lightly browned.
Let the casserole rest for 10 minutes before slicing.