For the filling:
Melt 1 tablespoon of butter in a large pan over medium-high heat. Add onion, carrot and celery and cook for 5-7 minutes until softened.
Reduce heat to medium-low; sprinkle flour over vegetables. Cook for 5 minutes, stirring frequently. Stir in milk and broth. Increase heat to medium-high; bring to a boil. Reduce heat, and simmer 5 minutes or until thickened.
Add chicken, peas, salt, and pepper. If the sauce is too thick, add more chicken broth, 1 tablespoon at a time, until desired consistency is reached.
Pour the chicken mixture into a 9 inch square pan that's been coated in cooking spray.
Preheat the oven to 450 degrees F.
For the biscuits:
Combine all of the dry ingredients in a bowl. Stir in the buttermilk and butter until a dough forms.Gently stir in the cheese.
Drop the dough into 4 equal sized mounds over the chicken mixture.
Bake for 12-15 minutes or until biscuits are golden brown.
Sprinkle with parsley if desired and serve.