Preheat oven to 200c (180C fan). Pat the lamb dry then season with salt and rub with 1 tbsp of olive oil.
Heat an oven-safe pan to a high heat and quickly seal lamb fillets on all sides. Mix the thyme, oregano and sage with the remaining oil. Spread over the tops of the fillets.
Put the dish into the oven and cook for around 15 minutes if you like your lamb rare, and an extra 5-10 minutes if you prefer it less pink. If you have a meat thermometer you can check more thoroughly - 145°F/60°C is medium rare, 160°F/70°C is medium and 170°F/75°C is well done. Meanwhile, you can make the flatbread.
To make the flatbread
In a large bowl mix the flour, baking powder, ground coriander and salt together. Mix the oil, water and milk in a jug, make a well in the dry ingredients, pour in the wet and mix together.
Gently roll into a ball on a lightly floured surface – don’t over work, it’ll make the final result tough. Cut the dough into four even chunks. Work each piece in a round circle about 7 inches wide.
Put a nonstick pan on a high heat and cook each flatbreads for 30-60 seconds each side, so that it has just a tiny bit of colour – you don’t need longer. Wrap all the flatbreads in a warm, slightly damp tea towel as you work to keep them soft.To construct
When your meat is cooked it should still be a little pink in the middle but not red or raw looking. Remove from the oven and cover the dish with foil to let the lamb rest for a couple of minutes. Transfer to a board and slice the lamb into 1.5cm pieces.
Grab one of your flatbreads and sprinkle with coriander and a generous portion of lamb. Add a sprinkling of feta, tomatoes and olives. Fold your flatbread in to create your wrap.