1 tablespoon butter
1/2 cup chopped green onions
1/2 teaspoon garlic powder
1 (4 ounce) can diced green chiles
1 (10.75 ounce) can condensed cream of mushroom soup
1/2 cup sour cream
1 1/2 cups cubed cooked chicken breast meat
1 cup shredded Cheddar cheese, divided
6 (12 inch) flour tortillas
1/4 cup milk