Heat the oil in a large pan which has a lid, then add the onion and garlic. Fry for 5-6 mins on a low heat until they begin to soften.
Rinse the lentils under running cold water using a sieve.
Add the red bell peppers and quartered tomatoes to the pan and continue to cook for a few mins on a low heat.
Add the tomato paste to the pan and stir.
Add the vegetable stock and rinsed lentils to the pan. Return the lid and bring to the boil.
Reduce the heat and allow to simmer on low, with the lid in place for 20 mins or until the lentils are beginning to break down / become soft. Add a little water if the mixture becomes too dry. It's better to have too much liquid than not enough.
Add the harissa spice mix, seasoning and cavolo nero and stir the whole pan together to ensure all combined well.
Spoon the mixture into bowls and serve immediately or allow to cool and store in suitable containers.
The Cavolo Nero is added at the end to retain the nutrients. The heat from the stew will be enough to gently cook the leaves before serving.
Serve with steamed broccoli and garlic toasts for that something extra.