In a blender, combine the oyster sauce with the vinegar, mustard, ginger and garlic and puree. With the blender on, gradually add the remaining 6 tablespoons of vegetable oil.
Bring a medium saucepan of salted water to a boil. Add the snow peas and cook until bright green, about 1 1/2 minutes. Drain the snow peas, refresh under cold water and pat dry.
In a serving bowl, combine the snow peas, jicama, peppers, onion and shrimp. Add the dressing, toss well and season with salt and pepper. Sprinkle on the cilantro and serve with lemon wedges.