In a medium skillet, heat the oil over medium heat and sauté chorizo and onions until fragrant, about 3 minutes. Remove from heat, add the tomato paste and garlic. Stir well to coat the ingredients with the tomato paste.
Transfer this mixture, plus all the other ingredients except the kale, into the bowl of a slow cooker. Cover, and cook on low for 6 to 8 hours.
Uncover, stir in the kale and cook for 30 minutes more. Discard the bay leaf and season to taste with additional salt and pepper.