Preheat oven to 350°F. Melt butter in microwave (30 seconds at a time until fully liquid). Pour most of the melted butter into a 9x13 inch casserole dish, swirling to coat the bottom. Reserve about 1/4 of the butter for later.
Spread shredded chicken evenly across the buttered dish. Break up any large chunks. Pour frozen peas and carrots over the chicken and spread out evenly. Do not stir.
In a small bowl, combine garlic powder, onion powder, black pepper, and chili powder. Stir with a fork, then sprinkle evenly over the chicken and vegetables. Do not stir the layers together.
In a bowl, whisk together cream of chicken soup and chicken broth until smooth and pourable, breaking up all condensed bits. Pour evenly over the chicken and vegetables, letting it seep into the spaces.
In a clean bowl, combine milk and biscuit mix. Add only half of the seasoning packet (save the other half). Whisk until smooth - batter should be thicker than pancake batter but pourable. Pour evenly over the pot pie (it won't cover everything completely).
Sprinkle shredded cheddar cheese over the entire surface (1/4 to 1/2 cup depending on preference).
Bake for 55 minutes, or until the top is golden brown and the edges are bubbling. Timing may vary based on your oven - watch for golden color and bubbling edges.
Remove from oven. If reserved butter has solidified, melt it again. Stir in the remaining half of the seasoning packet. Use a pastry brush to paint this seasoned butter over the biscuit top.
Let rest for 10 minutes before serving. This allows the filling to thicken properly and prevents burning your mouth.