Chicken Enchiladas

1 tablespoon butter
1/2 cup chopped green onions
1/2 teaspoon garlic powder
1 (4 ounce) can diced green chiles
1 can cream of mushroom soup
1/2 cup sour cream
1 1/2 cups cubed cooked chicken
1 cup shredded Cheddar cheese, divided
6 (12-inch) flour tortillas
1/4 cup milk

Preheat oven to 350 degrees F. Lightly grease a large baking dish.

In a medium pan over medium heat, melt the butter and saut