Preheat the oven to 350°F.
Lightly coat a casserole dish with nonstick cooking spray.
Shred the cooked chicken into small, even pieces.
In a medium skillet, combine the diced tomatoes with green chilis, chopped green chilis, sour cream, taco seasoning, and cream of chicken soup.
Place the skillet over medium heat.
Cook the mixture until heated through, stirring frequently.
Do not allow the mixture to boil.
Add the shredded chicken to the skillet.
Add 1 c of the shredded cheese.
Stir until the chicken is evenly coated and the cheese is melted.
Place a generous layer of tortilla chips in the bottom of the prepared casserole dish.
Spoon half of the chicken mixture evenly over the tortilla chips.
Add a second layer of tortilla chips over the chicken mixture.
Spoon the remaining chicken mixture over the second layer of chips.
Sprinkle the remaining 1 c of shredded cheese over the top.
Bake for 20 to 25 minutes, or until the casserole is hot throughout and the cheese is fully melted.
Remove the casserole from the oven.
Let it rest for a few minutes before serving.
Garnish with sour cream and chopped green onions, if desired.
Serve warm.