Heat a skillet over medium high heat.
Add oil and onion and saute 2 minutes.
Add cabbage and turn in pan, sauteing it until it wilts, 3 to 5 minutes.
Add vinegar to the pan and turn the cabbage in it.
Sprinkle sugar over the cabbage and turn again.
Season with mustard seed, salt and pepper and reduce heat a bit.
Let cabbage continue to cook 10 minutes or until ready to serve, stirring occasionally.
