Heat oil in a large saucepan over medium-high heat. Add onion, bell pepper and garlic. Cook, stirring often, until the vegetables are just tender, about 5 minutes. Add turkey and cook, stirring often, until browned, about 5 minutes. Stir in tomatoes, beans, pumpkin, water, chili powder, cumin, smoked paprika, pepper and salt. Bring to a boil over medium-high heat, stirring occasionally. Reduce heat to low; cover and simmer, stirring occasionally, until the flavors meld, about 20 minutes, adding kale during the last 5 minutes of cooking. Ladle into 4 bowls; top each with 1 tablespoon sour cream. Garnish with cilantro, if desired.