Peel melon and cut into crescents.
Segment grapefruit by cutting away the peel and white pith and then cut and lift out segments.
In a bowl, combine melon, grapefruit, ginger, carrot, and jicama.
Combine dressing ingredients in a small bowl, and set aside.
Place sesame seeds in a small frying pan over medium heat; cook while shaking pan continuously, until lightly browned, 3 to 4 minutes.
(For time-saver purpose, toast these in your microwave).
Immediately remove from pan to cool.
Remove any skin and bones from fish.
Thinly slice fish across the grain to make pieces about 1 by 2 in.
Fan slices on a serving platter, alternating pink and white fish.
In a small bowl, combine limejuice, oil and white pepper and drizzle over fish.
Drizzle limejuice mixture over fish.
Mound salad mixture in center of fish.
Spoon dressing over the salad, and garnish with peanuts, sesame seed and green onions.