Preparation / Directions:
In a small bowl whisk together all dressing ingredients. Dressing may be made 1 day ahead and chilled, covered.
Cut lobster meat or shrimp into bite-size pieces. Trim peas and diagonally cut into 1/4-inch slices. Cut cabbage, jicama, and carrots into thin julienne strips. Diagonally cut scallion greens into thin slices, reserving white parts for another use. Lobster or shrimp and vegetables may be prepared up to this point 4 hours ahead and chilled separately, covered.
In a dry small heavy skillet toast sesame seeds over moderate heat, stirring, until golden, 1 to 2 minutes, and transfer to a small bowl to cool.
Just before serving, in a large bowl toss lobster or shrimp, peas, cabbage, jicama, and carrots with dressing and sprinkle with scallions and sesame seeds.