How to Make It
In a small bowl, mix the olive oil, lemon juice and vinegar. Season with salt and pepper. In a large bowl, squeeze the 1/2 lemon over the celery, fennel and apples and toss well.
In another large bowl, toss the watercress with 1/4 cup of the vinaigrette. Add the grapes, parsley and the remaining vinaigrette to the celery, fennel and apples and toss well. Arrange over the watercress and serve.