Heat the olive oil in a large pot over medium heat. Add the diced onion and cook for 5 minutes, until soft and translucent. Stir in the garlic and cook for about 30 seconds, just until fragrant.
Add the ginger, turmeric, cumin, coriander, paprika, and cinnamon. Stir well and let the spices bloom in the oil for another 30 seconds.
Add the diced sweet potatoes, red lentils, and vegetable broth. Bring everything to a gentle boil, then reduce the heat to a simmer. Cover and cook for 15-20 minutes, until the sweet potatoes are tender and the lentils have completely broken down.
Stir in the coconut milk, lime juice. Taste and add salt and pepper and/or adjust seasoning as needed.
Serve warm, topped with fresh cilantro and sour cream.
