In a large pot, heat the olive oil over medium heat.
Sauté the onion, garlic, ginger, and turmeric for a few minutes, until onions start to soften and become translucent.
Add the remaining veggies, and salt and sauté for several minutes longer.
Pour in the lemon juice, and stir to coat the vegetables.
Add the broth, cayenne and additional salt and, if desired bring to a boil, cover and boil for 10-15 minutes, or until the veggies are soft.
Use an immersion blender, or add the contents of the pot to a blender or food processor, puree until smooth and creamy.
Return the soup to the pot, and heat through.