Heat the oil in a large, heavy based casserole. Fry the onion, carrot and celery for 10 minutes until softened. Add the sweet potato and garlic and cook for a minute more.
Once the sweet potato is tender and the sauce thick and rich, add the lentils and beans, stir through and simmer until heated through.
To serve, add to bowls, top with a good dollop of soured cream, tortilla chips, cheddar and coriander leaves.