Preheat your oven to 350°F (175°C). Pour the melted butter into the bottom of a 9x13-inch baking dish, spreading it to cover the surface.
In a medium bowl, combine the shredded chicken with the salt, pepper, garlic powder, onion powder, poultry seasoning, and smoked paprika. Stir to coat the chicken evenly.
Spread the seasoned chicken in an even layer over the melted butter in the baking dish. Scatter the frozen mixed vegetables over the chicken.
In a separate bowl, stir together the cheddar biscuit mix, its reserved seasoning packet, the milk, and ½ cup of the shredded cheddar cheese. Mix until just combined, do not overmix.
Use a large spoon or an ice cream scoop to drop dollops of the biscuit dough over the layer of vegetables. The dollops do not need to be perfectly uniform.
In a bowl, whisk the condensed cream of chicken soup and the chicken broth together until smooth.
Carefully pour the soup mixture evenly over the entire casserole, including the biscuit topping. Do not stir the layers together.
Bake for 50 minutes. The topping should be golden and the filling bubbly. Check that the internal temperature reaches 165°F (74°C) in the thickest part of the casserole.
Sprinkle the remaining ½ cup of cheddar cheese over the top and bake for another 5 minutes, or until the cheese is melted. Let the casserole rest for 10 minutes before serving.