Preheat your oven to 375°F (190°C).
Pour the melted butter into a greased baking dish.
In a medium bowl, combine frozen peas and carrots with onions and celery.
Spread the shredded chicken in an even layer in the casserole dish.
Add the mixed vegetables evenly on top of the chicken.
In a separate bowl, combine the biscuit mix, milk, seasoning packet if included, and 1/2 cup shredded cheddar cheese. Mix until well combined.
In another bowl, mix chicken broth and cream of chicken soup until smooth and gravy-like.
Pour the creamy chicken broth mixture over the vegetables in the casserole dish without mixing.
Pour the biscuit mixture carefully over the broth mixture without mixing.
Bake in the preheated oven for 45 minutes to 1 hour until the biscuit topping is golden brown and the casserole is bubbling.
Remove from oven and let cool for a few minutes before serving.