Whisk all ingredients for vinaigrette except olive and pecan oils, if using. Slowly add oil, continuing to whisk. Set aside.
Combine apples, pecans, cherries and Le Gruyère cheese in salad bowl. Spoon in part of the vinaigrette, to moisten. Add additional salt, if desired, and toss. Divide mixture on 4 plates. Add mustard greens to salad bowl and toss lightly with small amount of vinaigrette. Pile greens over apple-cheese mixture and serve salads immediately.
*You may substitute pears for apples
** You may substitute watercress or arugula or a mixture of greens.