Blanch snow peas in lightly salted boiling water for 1 minute. Drain in a colander and immediately run under very cold water for 1 minute to stop cooking. Drain again and pat dry.
In a large bowl, whisk together yogurt, mayo, curry powder, mustard, lemon zest, salt, and lemon juice. Add chicken, snow peas, celery, and scallions to yogurt mixture and toss to combine. Season with pepper to taste. Sprinkle with peanuts to serve.