In a small skillet, sauté onion in oil until golden brown; cool slightly. Unroll crescent dough and separate into triangles. Please note: there will be two extra triangles that may be used to make dinner rolls. Spread 1 teaspoon of mustard on each triangle, divide onions equally and place one link on the wide end of each triangle. Carefully roll-up. Place on an ungreased baking sheet, bake at 350ºF for 15-18 minutes or until golden brown. Serve hot.