Put the lentils, onion, celery, garlic, ginger, chilli flakes, ground coriander, salt, turmeric, cumin seeds, tomatoes and stock in the slow cooker. Stir.
Replace the lid and cook for 4 hours on low or 2 hours on high.
Put the shredded greens on top and let them steam, covered, for about 20 minutes.
Mix into the curry, and serve with lime wedges, low fat naan bread and coriander leaves sprinkled over the top.
Video
Notes
This is quite a mild curry. If you'd like to add more heat, thinly slice one or two fresh chillis to garnish as desired.