Put the yogurt, lemon juice and turmeric in a large bowl and combine. Add the cod and leave to marinate for 30 minutes. Soak short wooden skewers in cold water to prevent them burning.
Meanwhile, start the dhal. Put the split peas in a large bowl and cover with plenty of cold water. Soak for 30 minutes.
Heat the olive oil in a medium saucepan and cook the onion and garlic, stirring, for about 5 minutes, until just beginning to soften. Stir in the red pepper and tomatoes and cook for a further 10 minutes. Add the turmeric, cumin, coriander, ginger and cinnamon, stir until well combined, and cook for 1 minute.
Drain the split peas and add to the pan, tossing well with the vegetables and spices. Pour over the stock and bring to the boil. Simmer for 50-60 minutes. You may need to top up with a little extra stock to ensure that the pan doesn’t go dry. The dhal is cooked when the split peas are tender and creamy and all the liquid has been absorbed.
About 10 minutes before the dhal is due to be ready, preheat the grill to high. Thread the marinated fish onto the skewers – about 3 pieces per skewer. Place on a foil-lined baking sheet and drizzle over the melted butter. Grill under a high heat for 7-10 minutes, turning frequently until they are golden and crispy around the edges. Serve with the dhal.