Combine the ingredients for the dressing. Refrigerate until ready to add to the salad.
Wash the lettuce, drain and dry by patting with paper towels. Refrigerate several hours before serving. Peel the grapefruit and oranges with a sharp knife to remove both the outer skin and the inner white pith. Cut out each section so it is free of any membrane. When ready to assemble the salad, tear the lettuce into bite-sized pieces. Bombine with the fruit, onion, and jicama in a large bowl. Pour the dressing over the greens; toss lightly to coat the lettuce mixture.
