1. Prepare peas according to package directions, simmering only until al dente; drain and let cool 1 hour.
2. Whisk together cilantro and next 6 ingredients in a large bowl. Add cooked black-eyed peas, bell pepper, and onion, tossing to coat; cover and chill 8 hours. Stir peaches and watercress into pea mixture just before serving.