Bring a large pot of water to a boil and add carrots and sweet potato. Reduce heat to low and let simmer until semi-tender, about 5 minutes. Add cauliflower, celery, garlic, and turmeric; stir well. Simmer, stirring every few minutes, until cauliflower is fork-tender but not mushy, about 15 minutes.

Meanwhile, heat olive oil in a frying pan over medium heat. Add onion, season with salt, and stir until golden, 5 to 7 minutes.

Stir sauteed onion, coconut cream, and dill into the soup. Season with salt and pepper. Remove from heat and pour mixture into a large bowl. Let cool slightly, 5 to 10 minutes. Stir in lemon juice. Taste and adjust lemon juice, salt, and pepper to taste.

Use an immersion blender to blend until smooth. Enjoy hot or refrigerate and serve cool.