Put the lamb shanks into large plastic container or bowl, add capsicum, garlic and onion and pour the red wine over the top. Cover and leave to marinate for a few hours or preferably overnight in the refrigerator.
Put the cumin seeds in a pre-heated frying pan over a medium heat. Stir while they toast for 3 minutes or so - they will start to smell aromatic and jump in the pan when ready. (Don't burn them.) Tip them into a mortar, then dry roast the coriander seeds in the same way and add them to the mortar. Grind the spices to a powder with the pestle.
Lift the lamb shanks out of the marinade and set aside. Strain the marinade through a sieve or colander, reserving the liquid.
Heat the oil in a large flameproof casserole dish and when hot, brown the shanks, in batches if necessary. Transfer to a plate. Preheat the oven to 180C (350F).
Add the vegetables (reserved from the marinade) to the casserole dish, along with the chili and cook for 8 to 10 minutes until the onion has softened a little. Meanwhile, mix the tin of chopped tomatoes and honey into the reserved marinade liquid.
Scatter the ground spices and flour over the vegetables in the casserole dish and stir. Pour in the marinade mixture and stir everything together. Add the lamb shanks and bring the liquid to the boil.
Cover with a lid and transfer to the oven for 2 hours minimum. Gently turn the shanks over after 1 hour. If you have time, turn the oven down to say 140C and cook for a further 2 or 3 hours. (Alternatively, you could transfer it all to a slow cooker at this point instead of using the oven, and cook for 7 hours or more).
When ready, transfer the shanks to a large, deep serving dish and keep warm. Put the casserole dish over direct heat on the stove top and bring to the boil. Bubble for 10 minutes to reduce sauce. Pour the sauce over the shanks and serve, garnished with coriander if you like.