Prep: Add the onion, corn, beans, quinoa, garlic, cilantro stems, spices, salt, crushed tomatoes, tomato paste, and vegetable broth to a slow cooker. Mix well, until everything is evenly distributed.
Cook: Cover the slow cooker and cook on low for 4 to 5 hours, or on high for 3 hours.
Season & Serve: Stir well and add additional salt to taste, if necessary. Serve warm; top with the remaining cilantro leaves and any additional toppings, as desired. Leftovers will keep in the fridge for up to 5 days, or in the freezer for up to 2 months.
Instant Pot: Follow the instructions as written, using the Slow Cook function.