In the bowl of a food processor, pulse together the parsley, scallions, and garlic until finely chopped. Add the spinach, sour cream, mayonnaise, dill, vinegar, mustard, salt, and pepper and process until smooth and creamy, about 30 seconds. Scrape down the sides of the bowl and process again. Transfer the mixture to a medium bowl and stir in the bell pepper. Chill until ready to serve. Enjoy!