For the lamb, combine the garlic, ginger, cumin, coriander, chilli powder, garam masala, yoghurt, lemon juice, salt and pepper in a large bowl.
Place the lamb onto a large baking tray and spread the marinade all over. Cover with cling film and refrigerate for at least two, but no more than 24 hours. Just before placing the lamb in the oven scrape off any marinade left on the lamb, otherwise it will burn.
Preheat the oven to 170C/320F/Gas 3. Roast the lamb for 3-4 hours, depending on the weight of the shoulder and how well-done you like it. Once the lamb is cooked, brush with a tablespoon of melted ghee.
For the red lentil dal, place the lentils, ginger and turmeric into a saucepan, cover with water and bring to the boil. Skim any scum from the surface, and then reduce the heat until the mixture is simmering. Simmer the lentils for 25-30 minutes, or until tender. Drain well.
Meanwhile, heat a frying pan until hot, add the ghee and the finely chopped onion, ground cumin, ground coriander and chilli powder and cook for 2-3 minutes. Add the garlic and fresh red chilli and cook for a further 1-2 minutes, or until softened.
Add the tomatoes and cook for 1-2 minutes, or until the tomatoes have broken down and the mixture has thickened slightly. Add the cooked, drained lentils and stir to combine. Season, to taste, with salt and freshly ground black pepper. Set aside.
For the flatbread, place the flour in a medium bowl, add the salt and stir. Add enough water until the flour mix comes to a dough. Knead until smooth and divide into four.
Roll out each piece into a circle and place on a hot griddle pan one at a time. Turn the bread over once charred marks have appeared and brush with melted ghee.
To serve, shred the meat from the cooked lamb and serve with the red lentil dal. Garnish with the fresh coriander. Serve the flatbreads on the side.