Blend the green tomatoes with the chilies, coriander, milk, garlic and salt until smooth. Heat oil over medium-high heat; add sauce and cook until reduced and seasoned, about 5 minutes. Stir frequently. Remove from heat, add sour cream, and set aside. Fry or microwave tortillas until soft and flexible; dip one at a time into green sauce. Fill with chicken, roll and place into baking dish. Spread remaining sauce over enchiladas, garnish with cheese and onion, and bake at 350 degrees for 15-20 minutes or until warm.
From the Dinner Co-op