Peel the grapefruits and remove the individual segments (supreme) with a sharp knife. Place the tip of the knife between the fruit segment and the membranes that separate it from the next segment and cut inward on both sides to remove. Place the fruit into a bowl and save the pulpy membrane, which is full of juice, for the dressing.
Peel and julienne the jicama tossing it into the same bowl as the fruit. Discard the pulp and add the mustard to the juice. Whisk in the honey and the jalapeno and slowly whisk in the olive oil.
Toss the grapefruit and jicama with half of the dressing. Make a neat pile of greens on a dish and top with some of the salad. Drizzle some dressing around the plate, grind some pepper on top, sprinkle with sesame seeds.