1. Melt butter in large skillet over medium-low heat. Add mushrooms and green pepper, stirring frequently, for about 8 minutes or until the pepper is crisp tender. Add the flour and black pepper, mix well and continue to cook for about 3 minutes, stirring constantly.
2. Add the hot milk and chicken stock base and bring to a boil, stirring constantly. Reduce heat to low and simmer, stirring frequently, until slightly thickened, about 15 mintues.
3. Add the chicken and pimento and continue stirring until heated through.
4. To serve, spoon 1 cup of the mixture over each slice of toast.