To make the quick pickled onions, place the thinly sliced onion in a small bowl, and add salt, sugar and lemon juice. Massage together briefly. Set aside.
To make the dressing, combine the ingredients in a small jar and shake well. Set aside to infuse.
In a large mixing bowl, toss the vegetables and the onion (squeeze this out a little first) thoroughly. Add the dressing and toss again.