Sift the flour, sugar, salt and baking powder into a small bowl. Make a well in the centre and add the yoghurt. Using clean fingertips, gradually draw the flour into the yoghurt, mixing to form a small ball of soft dough.
Place the dough on a lightly floured surface and knead well for 5 minutes until you have a smooth ball. Lightly grease a small bowl with a little low-calorie cooking spray, place the ball of dough in the bowl and cover.
Leave in a warm place for approximately 45 minutes until the dough has increased in size very slightly and feels puffy when pressed.
While the dough is proving, make the keema pie filling. Spray a large frying pan with low-calorie spray and place over a medium high heat. Add the minced beef and brown for 4-5 minutes.
Add the onion, peppers and carrots and continue cooking for a further 3-4 minutes.
Add the ginger, garlic granules and curry powder. Stir well and then add the tomato puree. Pour in the beef stock and lemon juice, stir well and bring to the boil. Reduce the heat to low and allow to simmer, uncovered, for 20 minutes. The sauce should reduce and thicken. If you think it's still too runny, cook for a little longer.
Stir in the frozen peas, season with salt and pepper if needed, and divide the mixture between four 300ml ramekin dishes. Spread the mixture out evenly. Preheat the oven to 180°C.
When the naan dough has finished proving, turn the dough out onto a lightly floured surface. Roll out thinly and cut four 9cm diameter naan pie tops. You can use an upturned drinking glass with a 9cm diameter to do this if you don't have a 9cm plain pastry cutter. You will need to gather together the offcuts of dough and roll out again to make the fourth naan pie top.
Place the naan pie tops directly on top of the hot keema filling, sitting inside the rim of the dishes. Brush the naan pie tops with milk and sprinkle with a few sesame seeds.
Place the dishes on a baking tray and place in the preheated oven for 15-20 minutes, until the naan pie tops are golden, and the pies are piping hot.
Serve with steamed vegetables or other accompaniments of your choice.