Heat the olive oil in a large pot over medium heat.
Add the chopped onion, garlic, ginger, and turmeric. Cook for a few minutes until the onion softens and becomes translucent.
Add the potatoes, cauliflower, zucchini, carrots, and celery. Season with salt and pepper, then sauté for several minutes to begin softening the vegetables.
Pour in the lemon juice and stir to coat the vegetables evenly.
Add the broth and cayenne pepper, then stir to combine.
Bring the soup to a boil, then cover and let it cook for 10–15 minutes, or until all the vegetables are tender.
Remove from heat and blend the soup until smooth and creamy using an immersion blender or standard blender.
Return the soup to the pot and heat gently if needed.
Taste and adjust seasoning with additional salt, pepper, or cayenne as desired.
Serve warm, optionally topped with a spoonful of Greek yogurt.