2 large bunches of watercress, thick stems discarded
2 Belgian endives—halved, cored and thinly sliced lengthwise
1 cup flat-leaf parsley leaves
1 small red onion, halved and thinly sliced
Coarsely chop 1/4 cup of the olives and transfer them to a small bowl. In a mini processor, pulse the remaining 1/4 cup of olives with the garlic and rosemary until the olives are chopped. Add the vinegar and pulse twice to combine; add to the chopped olives in the bowl. Whisk in the olive oil and season with salt and pepper.
Using a sharp knife, peel the oranges, removing all of the bitter white pith. Working over a bowl, cut in between the membranes to release the orange sections into the bowl; drain the juice and reserve for another use. Add the watercress, endives, parsley and onion. Pour the dressing over the salad and toss well. Season with salt and pepper and serve at once.
The dressing can be refrigerated for up to 2 days.