Pop the skewers in a bowl or glass and cover with water. Leave them to soak – this will help keep them from burning when you grill the kebabs.
Spoon 1/4 of the yogurt into a dish. Peel and grate in the garlic and ginger. Add 2 tsp garam masala, a pinch of cayenne pepper (this is hot, so just use a little to start with unless you like things spicy) and a pinch of salt. Stir together to make a marinade. Add the diced lamb and turn to coat. Set aside to marinate for 10 mins.
While the lamb marinates, peel and finely chop the onion. Dice the tomatoes.
Warm a small pan over a medium heat for 1 min. Add ½ tbsp oil, the onion and tomatoes. Cook, stirring now and then, for 5 mins till the veg soften. Stir in 1 tsp turmeric, then add the rice and stir well so the rice is coated in the turmeric.
Pour in 300ml boiling water. Pop on a lid and bring the rice to the boil, then turn the heat right down and simmer for 8 mins till all the water has been absorbed. Take off the heat and let the rice stand in the pan, lid on, for 5 mins to steam and finish cooking the rice.
While the rice cooks, heat your grill to high. Line a baking tray or grill pan with foil. Lift the lamb out of the marinade and thread onto the skewers. Lay the lamb on a wire rack set on the grill pan (if you have one. If not, put the kebabs directly on the foil on the baking tray.
Slide the skewers under the grill for 8-12 mins, turning a few times, so they brown all over and cook them lamb through.
Fluff the rice with a fork and spoon onto 2 warm plates. Add a handful of baby leaf spinach to the plates and top with the lamb skewers. Serve with the rest of the yogurt on the side.