To make it on the stove:

1. Heat the olive oil in a Dutch oven to soup pot to medium. Add the carrots and onion and sauté 4-5 minutes or until slightly soft. Stir in the garlic, tomato paste (if using), cumin, coriander, salt, turmeric, black pepper, cinnamon and cayenne pepper and sauté 30-60 seconds or until fragrant. Add the lentils and stock and bring to a simmer. Add the potatoes.
2. Let soup simmer 25-30 minutes, stirring occasionally, until lentils and potatoes are tender. Stir in the coconut milk, lemon zest and juice and ½ of the cilantro. Taste and adjust the seasoning, if necessary.
3. Serve soup in bowls and top with remaining cilantro.

To make it in the slow cooker:

1. Place the carrots, yellow onion, garlic, tomato paste (if using), cumin, coriander, salt,  turmeric, black pepper, cinnamon, cayenne pepper and dried lentils in the bowl of a slow cooker. Cook on high 2-3 hours or low 4-5 hours or until lentils are tender. 
2. Add the potatoes and cook another 30 minutes on high or 1 hour on low or until slightly tender. Stir in the coconut milk, lemon and half of the cilantro. Taste and adjust seasoning, if necessary.
3. Serve soup in bowls and top with remaining cilantro.