Pre-heat oven to 400°F.
In a large saucepan, over medium heat, melt butter.
Add mushrooms, carrots and onion; cook and stir until tender.
Stir in flour until blended; gradually stir in broth and milk.
Bring to a boil, stirring constantly; cook and stir 2 minutes or until thickened.
Stir in chicken, peas, pimientos and salt; heat through.
Transfer to a greased 11 x 7-inch baking dish.