Preheat oven to 375 degrees. Mix the sugar, margarine, molasses, crystallized ginger and egg in a large bowl. Stir in the flour, ground ginger, baking soda and salt. Stir in the pecans. Drop the dough by rounded tablespoonfuls about 5 cm apart onto ungreased cookie sheets. Press a pecan half in the center of each cookie, if desired. Bake for dozen to 14 minutes, or until almost no indentation remains when touched in the center. Immediately remove from the cookie sheets. Cool on wire racks. Makes 2.5 to 3 dozen.