Preheat the oven to 200ºC.
Cut the squash by half and long side. Put on an oven tray, skin side up (don't need to be peeled) and roast 40 minutes until the flesh is soft. Remove from the oven and leave it to cool down a little bit.
Meanwhile in a pot, saute the leek until fragant and translucid, about 10 minutes. With spoon, remove the flesh of the pumpkin and add to the pot, discarding the skin.
Add ginger, rosemary, salt and pepper and cover with water. Bring to boil and leave it simmer for 20 minutes.
Blend it with a food processor or a hand blender and serve immediately with some of the roasted pumpkin seeds.