Put the lamb shanks in a large bowl with the garlic, rosemary, thyme, dried oregano, cinnamon, bay leaves, lemon juice (drop in the juiced halves as well), and olive oil. Season well, then toss everything together. If you have time, chill overnight.
Heat the oven to 190C/170C fan/ gas 5. Tip the potatoes and peppers into a large roasting tin, then pour over the wine. Remove the lamb from the marinade and set aside, then pour the leftover marinade over the veg. Toss to combine, then arrange the lamb on top of the veg. Cover tightly with foil and bake for 2 hrs 30 mins. Remove the lamb from the tin, turn all the veg over, then turn the lamb over and return to the tin on top of the veg. Drizzle over a little more oil, if the tin seems dry. Bake for 30 mins more, uncovered, until the lamb is falling off the bone and the potatoes are golden around the edges. Leave to rest for 5 mins, then scatter over the feta and fresh oregano, if using.