1.Boil, steam or microwave potatoes until tender; drain. Halve.
2.Meanwhile, rub both sides of beef with celery salt. Cook beef on heated oiled grill plate (or grill or barbecue), uncovered, until cooked as desired. Cover beef; stand 5 minutes, then slice thinly.
3.Blend or process a quarter of the spinach with parsley, mustard, oil, rind, juice and sugar until smooth. Season to taste with salt and pepper.
4.Combine potatoes, beef, remaining spinach, tomatoes and beans in a large bowl. Drizzle with dressing.