In a medium bowl, stir together the tomatillo verde salsa, sour cream, and half of the cheese.
Pour 2 cups of the sauce into another bowl. Set aside. (This is to pour over the top of the enchiladas later)
Stir in the shredded cooked chicken into the original batch of sauce.
Add 2 tablespoons of the reserved sauce to the bottom of a 9-inch x 9-inch baking dish.
Place roughly 1/4 cup of the chicken mixture in the center of each tortilla. Roll up each tortilla and place seam-side down in the baking dish.
Pour the reserved sauce evenly over the top of the enchiladas. Sprinkle the remaining cheese evenly over the top of the enchiladas. Bake in a preheated oven for about 20 minutes until the sides are bubbly and the cheese is melted on the top. Garnish with chopped, green onions, cilantro, or chopped avocado and serve.