In a large pot, heat the olive oil over medium heat. Add the leeks and garlic and cook, stirring occasionally, until softened, about 5 minutes.
Add the cumin, paprika, salt, and pepper and cook, stirring, for 1 minute.
Add the vegetable broth and diced yam and bring to a boil. Reduce the heat to low and simmer, stirring occasionally, until the yam is tender, about 10 minutes.
Stir in the coconut milk and simmer for 5 minutes more.
Using an immersion blender, blend the soup until creamy. Taste and adjust the seasoning if necessary.
Serve the soup garnished with cilantro, if desired.