Make the infusion: Combine water and hibiscus flowers in small saucepan and bring to a boil. Turn heat down and simmer, uncovered for 10 minutes. Strain and cool completely, reserving jamaica flowers. Makes a bit over 1/2 cup.
Make the vinaigrette: In medium bowl, combine jamaica infusion, mustard, salt and pepper. Make sure salt is dissolved. Start whisking in olive oil very slowly until dressing is emulsified. Correct seasonings.
Make the salad: In large bowl, arrange lettuce, green apple, grapes and a few of the reserved jamaica flowers. Drizzle with vinaigrette and toss very well. Sprinkle with pepitas and serve immediately.