Chicken Prep: Season and bake or BBQ the boneless chicken breasts to your liking. Cool and cut chicken into bite size cubes and place in a mixing bowl. Add enough enchilada sauce to coat the chicken thoroughly. Set aside.
On the stove, place refried beans in a sauce pan. Stir in milk, taco seasoning, green chilies and onion. Heat bean mixture through until blended, turn off heat. Set aside.
Reserve approximately 1 to 1 ½ cups enchilada sauce in a small baking dish. Set aside.(this will be used to coat the corn tortillas in the layering process).
Layering Process: In the 13 x 8 x 2 inch baking dish, take 1 corn tortilla at a time, running both sides through the reserve enchilada sauce and place in the baking dish covering the bottom.
Layer 1: Spread a layer of the bean mixture over the tortillas. Then place a layer of the cubed chicken over the bean mixture. Then place a light layer of cheese over the chicken. Finish with another layer of tortillas coated in enchilada sauce over the top of the chicken and cheese.
Layer 2: Repeat step 5, but instead of finishing with tortillas, finish with a generous layer of cheese to completely cover the chicken.
Place in a 325 degree oven for 20 to 25 minutes, until heated through and the cheese is melted. Remove from oven and allow to rest for 5 minutes before cutting.
Cut into desired portions and top with sour cream.