Peel and section grapefruit and oranges over a bowl; reserve any juices.
For dressing, in a screw-top jar combine reserved fruit juices, salad oil, lemon peel, lemon juice, sugar, mustard, and pepper. Cover; shake well.
Place greens on a large serving plate. Arrange fruit and jicama atop greens. Drizzle dressing over top. Serve immediately. Makes 10 side-dish servings.