Preheat oven to 350f degrees. Spray a 9x13-inch baking dish with nonstick cooking spray
Heat olive oil in a large skillet over medium heat. Add in onion and saute for about 5 minutes (until tender.)
Stir in garlic and saute for another minute.
Stir in diced chicken, green chiles and sour cream.
Season the mixture with salt and pepper. Continue to stir until warmed through (about 5-6 minutes.) Take off heat.
Wrap corn tortillas in a paper towel and warm in the microwave for about 30 seconds.
Spoon about 1/4 cup of the chicken mixture into each tortilla. Roll up and place seam side down into prepared baking dish. You should be able to get about 10-12 enchiladas from this.
In the same skillet, over medium heat, melt 2 tablespoons butter. Whisk in flour until thickened.
Slowly pour in milk and whisk until sauce gently boils and thickens. Season with salt and pepper (note: I like to use garlic salt here)
Whisk in softened cream cheese. Continue to whisk until smooth.
Pour sauce over prepared enchiladas.
Top with shredded Swiss cheese. Sprinkle dried parsley on top (optional)
Bake covered for about 25-30 minutes until heated through and bubbly.
Notes
Corn tortillas like to split open. If you warm them up a bit first, it helps to keep them from splitting while you wrap them up. However, you can avoid all of that by using flour tortillas.