In a food processor, add the spinach and pulse a few times until chopped very small. Add the processed spinach, drained chickpeas, and chopped onion into a large bowl.
In the food processor, add the lime juice, cilantro, mustard, sugar, garlic, cumin, and oil. Process until smooth.
Pour the dressing on top of the spinach and chickpea mixture and stir well. Add salt and pepper to taste.
Let stand for at least 10 minutes to let flavors develop. Serve over cooked pasta or rice.