Drizzle olive oil in a large pot over medium heat. Add the diced onion and cook until onions release some moisture, about 5 minutes. Stir in garlic, sweet potato, smoked sausage, and chickpeas. Add paprika, coriander, ground chipotle pepper, cumin, and salt. Cook for another 5 minutes, stirring once or twice.
Pour stock into the pot and bring to a simmer. Cook until sweet potato has softened, 10 to 15 minutes. Taste and add more salt, if needed. Stir in the kale (or spinach) and cook for 1 minute until kale has wilted. Ladle into bowls and top with crumbled feta cheese, if using, and freshly ground black pepper.
