Prepare pasta according to package directions; drain. Rinse the pasta under cold running water until cool and drain thoroughly. Preheat oven to 350 degrees F. In small bowl, stir together the cornstarch and 2 tablespoons of the milk until the cornstarch is dissolved. Heat the remaining milk and the chicken broth in a small saucepan over medium heat. Stir in the cornstarch mixture and heat, stirring, until the sauce is simmering and thickened. Add the salt and pepper and simmer 3 minutes. Pour the sauce into a bowl, add the peas, mushrooms, pimentos, chicken (if using), 1/2 cup of the Parmesan cheese and the cooked pasta. Stir the sauce in until it and the vegetables are evenly distributed. Transfer to a baking dish. Stir 1/4 cup of the Parmesan cheese and the bread crumbs together in a small bowl and sprinkle the mixture over the pasta. Bake until the sauce is bubbling and the topping is golden brown, about 15 minutes. Serve hot, passing additional grated Parmesan cheese if desired. (With chicken) Each serving provides: 440 Calories; 29.8 g Protein; 61.9 g Carbohydrates; 7.3 g Fat; 44.6 mg Cholesterol; 486 mg Sodium. Calories from Fat: 15% Copyright National Pasta Association (http://www.ilovepasta.org) (Reprinted with permission)