Heat the olive oil in a large pot over medium heat.
Add the diced onion and sauté for 4-5 minutes until softened and translucent.
Stir in the minced garlic, grated ginger, ground turmeric, ground cumin, and black pepper. Cook for 1-2 minutes until fragrant.
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 15-20 minutes until the cauliflower is very 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 blend until creamy.
Return the pureed soup to the pot over low heat. Stir in the coconut milk, sea salt, and lemon juice.
Heat gently for 3-5 minutes until warmed through, adjusting seasoning to taste.
Serve hot, garnished if desired.