In a large skillet melt butter. Add onion, celery, and carrot, and cook until onion is softened and transparent. About 4-5 minutes.
Add flour, stir and cook for 1-2 minutes.
Whisk in chicken broth and half and half.
Add cream cheese and cook until thickened.
Stir in chicken and peas and remove from heat. (If using frozen peas, can leave on heat for 2-3 minutes to allow peas to thaw, however don't allow to boil or overheat)
Prepare pie crust and add filling. Bake according to pie crust instructions.