In a medium bowl mix together one can of green enchilada sauce, sour cream, milk and onion. Mix until blended.
Preheat oven to 350 degrees.
On a microwave safe plate place 12 white corn tortillas and cover with a clean cloth. Place in microwave and heat for 2 minutes on high heat.
Remove one tortilla at a time. (Be careful they will be VERY hot.) Lay tortilla on flat surface. Place a good size pinch of cheese down the middle of each tortilla. Follow with Two Tablespoons of shredded chicken.
Starting from the outer edge of one side of the tortilla fold over the chicken and cheese and roll to the other edge of the tortilla.
Place seam side down in a 9 x 13 baking dish.
Continue filling tortilla's until they are all filled and in the baking dish.
You may have to lay some of the enchiladas the opposite direction to squeeze them all in.
Pour creamy enchilada sauce over the top of each enchilada.
Top with remaining cup of cheese. Sprinkle with chopped green onion.
Bake at 350 degrees for 30-40 minutes until cheese is melted and sauce is bubbly.
Serve immediately. Garnish with sour cream or salsa.