Preheat slow cooker to low.

Place a large sauté pan over medium-high heat. Lightly coat the bottom of the pan with olive oil.

Brown the onion, carrots, and fennel in batches over medium heat. Season each batch with salt and pepper. Add the garlic to the last batch of vegetables and lightly sauté it for two minutes more. Transfer the vegetables to the slow cooker insert.

To the slow cooker, add Moroccan spice mix, canned tomatoes and their juices, tomato paste, stock, and rice.

Cover and cook on low for four hours. Add more stock if the soup gets too thick. Adjust the seasoning with salt and pepper.

Ladle the soup into bowls and serve alongside garnishes.