Preheat the oven to 200C/400F.
Line a baking sheet with parchment paper, add the halved pumpkin and roast for 20 min until the flesh is tender.
Peel the roasted pumpkin and add it into the food processor to obtain a puree. Transfer into a bowl.
While the pumpkin is roasting, prepare the chickpeas. Start by rinsing them with plenty of water and add them into a medium soup pot. Cover with water, add the baking soda, mix to combine and place over medium heat and bring to boil.
Reduce the heat to low and simmer for 20 minutes, until their skins fall apart and the chickpeas are very well cooked.
Place in a colander to drain, rinse with cold water to remove the baking soda taste, then transfer into the food processor.
Process to obtain a puree, then add the tahini, pumpkin puree, lemon, salt, and garlic and process to obtain a smooth mixture.
Add 1 tbsp olive oil into a skillet over medium heat, add the spices and heat for 1 minute stirring frequently, to enhance the flavours.
Add the spices and oil to the food processor, and pulse to incorporate.
Transfer the hummus into a bowl, smooth it with a spoon, drizzle with olive oil and garnish with Nigella seeds and serve.
Keep the hummus into a glass airtight container into the refrigerator for up to five days.