Add the spinach to the bowl of a food processor. Cover and pulse a few times until finely chopped. Transfer the spinach to a large mixing bowl, and add the garbanzo beans and onions.
To the same food processor bowl (no need to rinse), add the cilantro, garlic, lime juice, mustard, sugar, olive oil, and cumin. Cover and process until smooth, scraping down the sides of the bowl as needed.
Pour the dressing over the garbanzo bean salad. Stir until everything is evenly mixed and coated in dressing. Season with salt and pepper to taste.
Refrigerate for about 10 minutes to let the flavors develop. Enjoy this salad on its own or with your favorite meals.
Notes
If you don't have a food processor available, finely chop the spinach by hand. To make the dressing, peel and mince the garlic. Then, add all the ingredients is a mason jar, cover, and shake vigorously until combined.