Heat a large frying pan with a tight-fitting lid over a medium heat. Brush the lamb fillets on one side with a little of the oil. Add the fillets to the pan, oiled-side down, and fry for 3-4 minutes until nicely browned. Lightly brush the lamb fillets with a little more oil, then flip them over and continue frying for a further 1 minute. Transfer the lamb fillets to a plate and set aside.
Add 1 tablespoon of the oil to the pan and heat. Add the potatoes and fry, turning occasionally, for 5 minutes or until golden and they start to soften.
Add another 1 tablespoon of oil to the pan. Add the zucchini, onion, peppers and garlic and continue frying, stirring occasionally, for 5 minutes or until all the vegetables are tender.
Meanwhile, mix the remaining oil with the vinegar in a small jug or bowl. Return the lamb fillets to the pan, placing them on top of the vegetables, and pour in the oil and vinegar mixture. Crumble the feta cheese over the top. Reduce the heat to low, cover the pan with a lid and cook for about 5 minutes for medium-rare or 7 minutes for medium.
Uncover the pan and scatter the mint over the top. Season with freshly ground black pepper to taste. Serve at once, straight from the pan, with a drizzling of the pan juices.
Variation: Pork and fennel is a popular flavour combination in Greece. Replace the lamb fillets with 4 well-trimmed pork loin chops and the zucchini with 2 thinly sliced fennel bulbs. Use a white onion instead of the red and add 1 teaspoon fennel seeds to the vegetables in step 4.
Each serving: 30.5 g protein, 25 g fat of which 8.5 g saturates, 15 g carbohydrate, 5 g fibre, 420 Calories