Whisk first 9 ingredients in medium bowl to blend.
Add enough water to large saucepan to reach depth of 1/2 inch. Bring to boil; add sweet potatoes and cook until just tender, about 5 minutes. Drain; cool.
Mix sweet potatoes, dressing, peas, and green onions in large bowl. Season salad with salt and pepper. (Can be made 4 hours ahead. Cover and refrigerate.) Sprinkle salad with peanuts and serve.