Preheat the oven to 200°C. Line the baking pan with parchment paper. Set aside.
Cut the top of the pumpkin and then carefully halve the pumpkin*. Hallow out all the seeds using a spoon. Slice the pumpkin, cut into cubes, and place them onto the baking pan.
Peel the yellow onion and cut it into quarters. Peel 3 cloves of garlic. Place cut onion and peeled garlic to the pan with pumpkin and drizzle with olive oil. Season it all with black pepper and marjoram. Toss everything until it's all coated.
Roast for about 35 minutes, until the pumpkin is soft**.
Remove the pan from the oven and put the roasted pumpkin, onion, and garlic into a blender (if using a plastic blender, let it cool slightly). Add vegetable broth, lemon juice, sea salt, and nutritional yeast. Blend until it’s smooth and creamy. If needed, add more vegetable broth or boiled water. Taste and add more salt or seasoning if necessary.
Pour the soup into a pot, bring to boil, and simmer for about 5 minutes to combine the flavors.
Serve with your favorite toppings.