Preheat the oven to 350 degrees.
In an oven-safe pot, melt the butter and sauté the chopped onion, celery, and carrot until they become soft, which should take about 5-6 minutes. Stir in the chopped garlic and season with Italian seasoning and garlic powder.
Add the flour and cook for 2 minutes, stirring continuously.
Gradually pour in the chicken stock in thirds, allowing the stock and flour mixture to combine before adding the next portion. This gradual addition will help thicken the sauce.
Reduce the heat to low and add the milk, frozen peas, cooked chicken, and soy sauce. Taste and adjust the seasoning with salt and pepper to your preference.
Place the biscuits in a single layer on top of the mixture.
In a small bowl, combine the melted butter, Italian seasoning, and garlic powder. Brush the top of the biscuits with this mixture.
Cover the pot and bake in the preheated oven for 20 minutes, uncovering for the last 5 minutes to allow the tops of the biscuits to brown. The exact cooking time may vary depending on the size of your biscuits; you want the middle to be cooked and the tops to be golden brown. You can also cook the biscuits on a pan separately to have a crust on the top and bottom of the biscuits.