1. Preheat oven to 400°. Melt butter in a large saucepan over medium heat. Add green onions, salt, and pepper, and cook 1 minute. Add mushrooms, and cook 10 minutes or until tender. Add chili powder and flour, and cook 1 minute. Add milk, and simmer 5 minutes or until mixture begins to thicken; remove from heat. Add more chili powder, if desired. Add turkey, pimientos, and green chiles. Stir in sour cream.
2. Arrange 4 tortillas side by side in a microwave-proof dish. Cover with dampened paper towel, and microwave on HIGH for 30 seconds. Repeat with remaining tortillas.
3. Arrange 4 tortillas in a 10-inch pie plate, cover with half the turkey mixture, and sprinkle with 1 cup cheese. Repeat with remaining tortillas, turkey, and cheese. Bake at 400° for 20 to 25 minutes or until bubbly and golden brown. Garnish, if desired.