Heat olive oil in a large pot over medium heat.
Add the chopped onion and sauté for 5 minutes until translucent.
Add the minced garlic and grated ginger, cooking for another 2 minutes until fragrant.
Stir in the ground turmeric and ground cumin, cooking for 1 minute to release their aromas.
Add the chopped cauliflower florets to the pot and stir to coat with the spices.
Pour in the vegetable broth and bring the mixture to a boil.
Reduce heat to low, 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 creamy.
Return the pureed soup to the pot if needed, then stir in the coconut milk, black pepper, salt, and lemon juice.
Heat the soup gently over low heat for 3-5 minutes, stirring occasionally. Do not boil.
Taste and adjust seasoning if necessary before serving.