In a large pot, heat the coconut oil over medium heat. Add the diced onion and sauté for 3-4 minutes until softened. Add the minced garlic and cook for another minute.
Stir in the curry powder, cumin, and turmeric. Let the spices cook for about 30 seconds to release their flavors.
Add the rinsed lentils, diced sweet potato, coconut milk, diced tomatoes, and vegetable broth to the pot. Stir everything together and bring the mixture to a boil.
Once boiling, reduce the heat to low, cover, and let the curry simmer for 20-25 minutes, or until the lentils and sweet potatoes are tender.
Season with salt and pepper to taste. If the curry is too thick, add a little more vegetable broth to reach your desired consistency.
Serve warm, garnished with fresh cilantro