Preheat oven to 375º.
In a medium sauce pan, sauté garlic in butter over medium-high heat for about 1 minute.
Stir in flour and continue to stir while cooking for 2 minutes.
Combine the chicken broth, cumin, salt and pepper. Add to the butter/flour mixture, stirring constantly.
Bring to a simmer while continuing to stir.
Remove from heat and stir in the sour cream, salsa verde and cilantro.
Grease a 9x13 inch baking dish.
Add about ½ cup sauce to the bottom of the pan. Spread until bottom of the dish is evenly coated.
On a flat surface, lay out a tortilla. Add chicken, shredded cheese, and avocado, filling to the end of the tortilla.
Roll the enchilada and place, seam side down, in the baking dish. Repeat until all tortillas and filling are used up.
Pour the remaining sauce over the enchiladas. Cover with remaining cheese (1 to 1-1/2 cups) and bake, uncovered, for 20 minutes, or until cheese is bubbling.