In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and cook for another minute, until fragrant.
Add the diced potatoes and vegetable broth to the pot. Bring to a boil, then reduce heat and simmer for about 15-20 minutes, or until the potatoes are tender.
Once the potatoes are soft, add the chopped spinach and simmer for an additional 5 minutes.
Remove the pot from heat and use an immersion blender to puree the soup until smooth. (Alternatively, you can carefully transfer the contents to a blender in batches.)
Stir in the coconut milk, lemon juice, and lemon zest. Mix well and season with salt, pepper, and nutmeg if using.
Return the soup to a gentle heat for a few more minutes to warm through, adjusting seasoning as needed.
Serve hot, garnished with croutons or toasted seeds for added crunch.
Notes
For a richer flavor, use homemade vegetable broth.