Irish beef Stew, garden peas, lemon and mint

600 g stewing beef such as blade steak (Irish beef), at room temperature
3 tbsp olive oil
2 leeks, cut into in rings
1 lemon (scrubbed)
500 ml chicken broth (homemade, from a pot or a stock cube) + extra
2 sprigs of fresh mint
100 g of feta cheese
300 g fresh garden peas (or frozen*)
salt and freshly ground black pepper
casserole dish