In a large skillet, heat oil. When hot add chicken and saute 4 to 5 minutes until about halfway cooked. Add mushrooms and continue to saute until chicken is lightly browned and cooked through (juices run clear). Stir in the milk, soup, mushrooms, pimentos, onion powder and pepper. Bring all to a boil. Cover skillet and reduce heat. Let simmer for 2 to 3 minutes. Stir together and serve.