Heat a couple of tablespoons of olive oil in a large pot over medium heat. Add the chopped onions and minced garlic, sauté until they turn soft and golden brown.
Add the sweet potatoes to the pot along with the curry powder, ground cumin, garam masala, cayenne pepper, and ground turmeric. Stir until the sweet potatoes are well coated with the spices.
Pour in the coconut milk and broth. Increase the heat and bring the mixture to a boil. Once boiling, reduce the heat and let it simmer for approximately 30 minutes, or until the sweet potatoes are tender.
While the soup is simmering, prepare the chickpea garnish. Toss the chickpeas in a tablespoon of olive oil, and a pinch each of cayenne pepper, cumin, and salt. Spread them evenly on the prepared baking sheet and bake for 15-20 minutes, or until they're crispy and golden brown.
Once the sweet potatoes are tender, blend with soup in an upright blender or with an immersion blender. Season with salt and pepper to taste. You can add more broth or water if you prefer a thinner soup.