Preheat your oven to 375°F (190°C).
In a large skillet over medium heat, melt the butter.
Sprinkle in the flour, salt, black pepper, garlic powder, and onion powder. Stir until it forms a smooth paste (roux) and cook for about 1-2 minutes until bubbly and slightly golden.
Slowly whisk in the chicken broth and milk, stirring as the mixture thickens, about 3-5 minutes.
Stir in your cooked chicken, frozen peas and carrots, and corn if using. Mix well and remove from heat.
Transfer the chicken mixture into a greased 9×13-inch baking dish, spreading it evenly.
Open the can of biscuit dough, separate into individual biscuits, flatten each slightly, and arrange on top of the chicken mixture, leaving space for expansion.
Bake for 25-30 minutes, or until the biscuits are golden brown and thoroughly cooked.
Let the casserole rest for about 5 minutes before serving.