Heat the oil in a large sauté pan over medium-high heat. Add the onions, season with salt and pepper, and cook, stirring, until the onions are golden, 10 to 12 minutes. Add the sugar and cook, stirring, for 2 minutes. Add the vinegar and parsley and cook, stirring, for 1 minute. Remove from the heat, cool, and serve.
Can be stored in an airtight container in the refrigerator for up to 1 week.
Yield: about 1 1/2 cups