Saute the onion in hot oil in skillet over medium high heat with the salt, pepper, and cayenne, cook stirring often, for about 10 to 12 minutes, or until the onions are golden. Add the sugar and cook for 2 minutes, stirring constantly. Add the vinegar and parsley and cook for 1 minute. Remove from heat, cool and serve.
Can be stored in airtight container in the refrigerator for up to 1 week.