Preheat the oven to 425 F/ 220 C/ gas mark 7. Arrange the squash slices in a single layer on a large baking sheet lined with parchment paper. Season and drizzle with a little oil. Pop in the oven for 30-40 minutes or until the squash is lightly browned and fully cooked. Remove from the oven and peel off the skin. Set aside.
Whilst the squash is in the oven prepare the soup. In a large pot heat up the oil, add the bay leaf, garlic, ginger, onion and cook for 3-4 minutes over a medium heat stirring often. Add the lentils, spices and seasoning and cook for 2 more minutes.
Pour in 2 cups of the stock, cover and simmer gently for 15 minutes. Remove from the heat, discard the bay leaf, add in the roasted squash, more stock (still not all) and puree until smooth. Add more stock if needed, adjust seasoning as necessary and serve.
You can roast the squash in advance and once cooled, peel and refrigerate, covered for up to 2 days.
Spices and herbs: In addition to the spices I've used (or instead of) you could add smoked or sweet paprika, cumin and chili into this soup. Scatter freshly chopped cilantro or parsley before serving if you like.
Add the stock gradually according to preference.
It is important to remove the soup from the heat before adding in the butternut squash. The squash will have fully cooked in the oven so by cooking it further in the soup some of its rich flavour may be lost.
Serve with toasted pumpkin seeds or sunflower seeds with a drizzle of coconut milk or cream. Delicious also with grilled ciabatta bread or croutons.
Freeze individual portions in airtight containers.