For DRESSING: Whisk together vinegar, soy sauce, oil, sugar and mustard in small bowl. Season with cayenne pepper. (Can be prepared 1 day ahead. Cover and leave at room temperature).
For SALAD: Blanch bean sprouts in boiling water 30 seconds. Drain and refresh in cold water. Drain. Bring large pot of salted water to boil. Add noodles and boil until tender, stirring occasionally, about 3 minutes.
Drain noodles. Refresh in cold water. Drain and place in large bowl. Add sesame oil and toss to coat. (Can be prepared up to 6 hours ahead. Cover and refrigerate bean sprouts and oriental noodles separately.) Add bean sprouts, shrimp, cucumbers and onions to noodles. Drizzle with dressing. Toss gently to combine. Line platter with cabbage leaves and mound salad in center.