1. Prepare peas according to package directions; drain and let cool 1 hour.
2. Whisk together sugar and next 5 ingredients in a large bowl. Add 1/4 cup oil in a slow, steady stream, whisking constantly until smooth. Add cooked field peas, bell pepper, onion, and celery, tossing to coat; cover and chill 8 hours.
3. Sauté ham in 1 tsp. hot oil in a small skillet over medium-high heat 4 to 5 minutes or until lightly browned. Stir into pea mixture just before serving.