Preheat the oven to 30 degrees. Lightly spray 2 13x9 inch casserole dishes with cooking spray.
In a large skillet, heat the oil over medium heat. Add the onion and cook until translucent. Stir in the flour and cook for another minute. Blend the broth, milk, garlic powder, thyme, lemon zest, salt, nutmeg and pepper together and gradually add to the flour/onion mixture stirring constantly. Bring to a boil and reduce the heat to simmer and cook until thicken.
Stir in the chicken and frozen peas and carrots, heat thoroughly. Stir in the noodles and cheese.
Divide equally into the 2 casserole dishes.
In a small bowl combine the cornbread stuffing mix and melted butter. Sprinkle over the top of the chicken casseroles. Bake for 10 minutes or until the tops are brown.