Heat the oil in a large frying pan and brown the lamb shanks on all sides. Remove from the pan and place in the slow cooker.
Reduce the heat and add the onions. Fry for 10 to 15 minutes until the onions have softened and are beginning to brown. Stir in the garlic, sugar and vinegar and cook for another minute or two.
Tip the onions on top of the lamb shanks, then add the herbs, wine (or port) and stock.
Pile the peppers on top, cover and cook on high for 8 hours. Season to taste.
If you do not have a slow cooker you can cook this dish in a preheated oven 180℃ (160℃ fan)/350°F /gas mark 4 for 2–3 hours. Check half way through the cooking time and add a little extra stock if required.Nutrition information is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)