Cut the meat into pieces of about 1½ cm. Heat 2 tablespoons of olive oil in the casserole dish and fry the meat on a high heat for 5 minutes until golden brown. Sprinkle with salt and pepper to taste and remove the meat from pan with a slotted spoon.
Heat the rest of the olive oil in the pan, add the leek and stir-fry for 2 minutes. Zest and juice the lemon. Put the meat back in the pan together with the lemon juice (keep the zest for later) and 500ml chicken broth. Bring to boil. Put the lid on the pan and simmer the meat for about 2 hours until fully cooked (longer if necessary). Use the smallest burner of the stove and if necessary, insert a flame distributor. Stir occasionally. Add some extra hot chicken stock if necessary.
Season the stew with salt and freshly ground black pepper. Finely cut the mint leaves. Add the garden peas 3 minutes before serving, crumble the feta above and garnish the stew with the mint and lemon zest.
Serve the stew with boiled new potatoes or potatoes.
*If using frozen peas, boil them in advance 2 minutes before you add them to the stew. This cools the meat less, and stays nice and tender