Preheat oven to 425°F. Spray a 2.5–3-quart baking dish with cooking spray.
In a bowl, whisk together chicken broth and half-and-half. Set aside.
In a large skillet, melt butter over medium-high heat. Add onion, carrot, and celery. Sauté for 10 minutes.
Stir in flour and cook 1 more minute.
Reduce heat to medium, gradually add the broth mixture, stirring until thickened (5–6 minutes). Do not boil.
Stir in salt, pepper, chicken, and peas. Transfer to prepared baking dish, cover with foil, and bake for 10 minutes.
In a bowl, mix Bisquick, buttermilk, cheese, and parsley until a soft dough forms. Add extra buttermilk as needed.
Remove the filling from the oven and give it a stir.
Use a scoop to drop about 8 biscuits on top of the hot filling.
Bake uncovered for 12 minutes, or until biscuits are golden and cooked through.
Mix melted butter and garlic powder, and brush over warm biscuits before serving.
