In a small mixing bowl combine vinegars, yogurt, olive oil, sugar, salt, horseradish, celery and mustard seeds, and parsley. Set aside. In a large glass bowl, combine cucumbers, bell pepper, red onion, serrano (or jalapeño) and tomatoes. Pour the yogurt mixture over the vegetables and then season with salt and pepper to your liking. Fold together, stir and cover with plastic wrap. Refrigerate for several hours. Use a slotted spoon for serving to drain excess liquid.