Place cut side of the marrow down in a lightly oiled baking pan. Bake at 180 C / Gas mark 4 for 30 minutes, or until a sharp knife can be inserted with only a little resistance. Remove marrow from oven, and set aside to cool enough to be easily handled. Shred flesh of the marrow with a fork.
In a large soup pot, sauté onions and garlic in olive oil. Add curry powder, cumin and turmeric. When onions are transparent, add stock and lentils and bring to the boil. Reduce to simmer and add chopped tomatoes and juice.
If using brown rice, add the rice 10 minutes after adding the lentils, if using white rice, add rice after 25 minutes along with the sweetcorn.
After 35 minutes, add the macaroni and spaghetti marrow. Simmer until rice and pasta are cooked.