Melt the margarine in a Dutch oven. Add the carrots, onions and celery all at once and saute until soft but not brown. Add flour and stir to combine. Cook until mixture begins to turn a light-brown color. Over medium high heat, add the chicken broth a little at a time. Stir and continue to cook and stir with a whisk until a thick base if formed. Add half and half being careful not to let it boil. Add cheese, stirring until melted. Just before serving add parsley. Garnish with diced tomatoes and jalapenos, if desired.