Preheat oven to 375 degrees.
Pour 1/2 cup enchilada sauce in the bottom of your baking dish and spread to evenly coat.
Mix cheddar cheese and jack cheese in a bowl.
Lay out 8 corn tortillas and spread about a tablespoon of sour cream in each tortilla. Evenly distribute shredded chicken amongst the tortillas. Finally, sprinkle with about 1-2 tablespoons of mixed cheese leaving about 3/4 cup of cheese for topping.
Roll enchiladas up and place seal side down in the baking dish. Top enchiladas with remaining green enchilada sauce and sprinkle top with remaining cheese.
Bake enchiladas uncovered for 30-35 minutes until bubbly and cheese is melted.
Serve enchiladas with sliced avocado and a sprinkle of fresh cilantro (optional).