Heat olive oil in a large pot over medium heat.
Add chopped onions and sauté until translucent.
Stir in minced garlic and grated ginger, cooking for another minute.
Add cubed sweet potatoes and stir to combine.
Pour in the vegetable broth and bring to a boil.
Reduce heat and let simmer until sweet potatoes are tender (about 20 minutes).
Remove from heat and let cool slightly.
Blend the soup using an immersion blender until smooth.
Stir in coconut milk if using, and season with cumin, salt, and pepper.
Serve hot, garnished with pumpkin seeds.