In a stock pot, bring 3 - 4 boneless, skinless chicken breasts to a boil. When cooked through, remove and shred. Set aside. Save the chicken broth for later.
In a saucepan on medium high heat, melt 2 T butter then whisk in 2 T cornstarch. Whisk in 2 C chicken broth (from boiling the chicken). Bring to boil then reduce to a simmer for 5 minutes. Whisk in 3/4 C sour cream, 1/2 t cumin, 1/2 t salt, 1/2 t garlic powder and 1/4 t pepper. Add the meat of 2 large avocados and the juice of one lime. Either use a hand blender or put into a blender and blend until smooth.
In a saucepan over medium high heat, heat 2 T oil. Saute 1 medium chopped onion and 2 green chilis, roasted and thinly sliced until cooked through. You can also use a can of green chilis.
You'll also need 8-10 warm corn tortillas & 3 C shredded cheese.
In each tortilla, add a little avocado cream sauce, shredded chicken, sauteed onion mixture and shredded cheese. Wrap carefully and pack tightly in a greased baking dish. When finished, top with half of what's left of the avocado cream sauce and the rest of the shredded cheese. Cook in a preheated oven of 375° for 20 minutes. Remove from oven and top with remaining avocado cream sauce and sour cream, if desired.