Boil the artichokes in salted water for 20 minutes until they are giving but not collapsing then allow to cool. Slice lengthwise about ⅜ inch thick and put to one side. Meanwhile skin and quarter the onions, then toss in the olive oil and balsamic vinegar, season with salt and pepper, and roast in a medium to hot oven 375°F until soft and sweet. Allow them to cool slightly. Mix the watercress, olives and parsley (parsley acts as a great marrier of disparate parts in a salad, the dating agency of the salad world).