Heat a large pot over medium heat. Add the onion, garlic, ginger and water. Cook until the onions are just tender and water has evaporated, about 3 to 5 minutes.
Add the curry paste and stir to combine with the onion mixture. Stir in the broth and coconut milk. Add in the lentils and cook for 8 to 10 minutes until the lentils are just tender, stirring often.
Add the cauliflower and sweet potato to the pot. Stir to combine, then cover with a lid and reduce the heat to medium-low. Cook for 15-20 minutes or until the vegetables are tender, stirring often.
Season with additional salt if needed, and divide between bowls. Top with cilantro, if using, and enjoy.