Preheat the oven to 425°F (220°C) and grease a medium-sized casserole dish with butter or cooking spray.

In a medium mixing bowl, whisk together the chicken broth and half-and-half until smooth and combined.

Sauté the chopped onions, carrots, and celery in a large skillet with butter for about 5-7 minutes until tender.

Sprinkle in the flour and stir it to combine, cooking for about 1 minute to create a roux.

Gradually pour in the broth mixture, whisking continuously until the filling thickens and bubbles.

Stir in the cooked chicken and frozen peas, mix well, and transfer to the greased casserole dish.

In a separate bowl, mix Bisquick, buttermilk, cheddar cheese, and parsley until just combined.

Drop spoonfuls of biscuit dough over the chicken filling and bake for 15-20 minutes until golden brown.

Remove from oven, cool slightly, and optionally brush biscuits with melted butter mixed with garlic powder.