Heat the olive oil in a large pot over medium heat.
Add the diced onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and ginger, cooking for another minute until fragrant.
Add curry powder, cumin, turmeric, and cayenne pepper. Stir for about 30 seconds to toast the spices.
Add the rinsed red lentils, coconut milk, vegetable broth, diced carrot, and red bell pepper. Stir to combine.
Bring the mixture to a boil, then reduce the heat to low and let it simmer for 25-30 minutes, or until the lentils are tender.
Once the soup has thickened, use an immersion blender to puree the mixture to your desired consistency. This step is optional; you can leave it chunky if you prefer.
Season with salt and pepper to taste. If the soup is too thick, you can add a bit more vegetable broth to reach your desired consistency.
Serve hot, garnished with fresh cilantro and a squeeze of lemon juice if desired.