Preheat Oven: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish with butter or non-stick spray.
Make the Filling: In a large bowl, combine the cooked chicken, cream of chicken soup, frozen peas and carrots, milk, garlic powder, onion powder, thyme, salt, and pepper. Stir until well combined.
Assemble the Casserole: Pour the chicken mixture into the prepared baking dish. Spread it out evenly.
Add Biscuits: If using refrigerated biscuit dough, open the can and cut the biscuits into quarters. Arrange the biscuit pieces evenly over the chicken mixture, covering as much surface area as possible. If using biscuit mix, prepare it according to package instructions, then drop spoonfuls of the batter over the casserole.
Bake: Place the casserole in the preheated oven and bake for 30-35 minutes, or until the biscuits are golden brown and the filling is hot and bubbly. If desired, sprinkle shredded cheddar cheese on top of the biscuits during the last 5 minutes of baking for a cheesy topping.
Serve: Once the casserole is done, let it sit for a few minutes before serving. Scoop out portions with a spoon, ensuring you get some of the chicken, vegetables, and biscuit in each serving.
