Heat the oil in a large deep pan over a medium low heat. Add the diced onion and a pinch of salt and cook for 10 minutes, stirring occasionally, until the onion is soft and translucent.
Meanwhile prepare the beetroot. If it is already cooked drain and coarsely grate. If fresh, wash and trim off the roots and stems, then grate. If the leaves are still attached you can use them too. Wash well and roughly chop, then add to the chilli five minutes before the end of the cooking time.
Add the grated beetroot to the onions and stir to combine. Cover and allow to sweat for 10 minutes, stirring from time to time.
Add the garlic, smoked paprika, cumin, oregano and chilli powder. Stir well and cook for 1-2 minutes until fragrant.
Add the lentils, chopped tomatoes, red kidney beans, soy sauce and cocoa powder and stir to combine. Add the water then bring to a simmer and cook, partially covered for 25 mins. Stir regularly and add a splash more water if it starts to dry out.
When its ready the lentils and beetroot will be tender. Add salt to taste, and more chilli if you like. Serve immediately.