Heat the olive oil in a large pot over medium heat.
Add the diced onion and sauté for 5 minutes until translucent.
Add the minced garlic and grated ginger, and cook for 1 minute until fragrant.
Stir in the ground turmeric, ground cumin, ground coriander, and black pepper. Cook for 1 minute to toast the spices.
Add the chopped cauliflower florets to the pot and stir to coat with the spices.
Pour in the vegetable broth, bring the mixture to a boil, then reduce heat to a simmer.
Cover and simmer for 15 minutes, or until the cauliflower is tender.
Remove the pot from heat and use an immersion blender to puree the soup until smooth. Alternatively, carefully transfer the soup in batches to a blender and puree until smooth.
Return the pureed soup to the pot, stir in the coconut milk and fresh lemon juice.
Heat the soup gently over low heat until warmed through. Season with salt to taste.
Ladle the soup into bowls and garnish with chopped fresh cilantro before serving.