In a large skillet, melt butter and add mushrooms and chopped pimentos. Cook and stir until mushrooms are tender, about ten minutes. Remove from heat.
Put in a small jar water, flour, bouillon, and pepper. Cover and shake, and pour into skillet with mushroom mixture.
Cook and stir over low heat until mixture thickens. Add chicken, stir well, and put on biscuits or toast or rice.