- Slice the onion thin, place in a bowl, add the juice of 1 lemon and set aside for 20 minutes 
- Quarter the green and red cabbage, remove the cores 
- Slice thin and place in to a large bowl 
- Julienne the carrots and place in to bowl 
- Pick the parsley leaves and place in to the bowl 
- Drain the onions, reserving the lemon juice, and add the onions to the bowl 
- Toss to mix all the vegetables through 
- Dress the slaw with mayonnaise, mustard, sugar, and mustard seed 
- Add reserved lemon juice as needed until slaw pops with brightness