1. Heat the oil in a very large saucepan over medium heat. Sweat onions in olive oil for a few minutes, add garlic and cooked for another minute. Add the turkey and cook, breaking it up well with a wooden spoon, until no longer pink, about 5 minutes.
2. Add the sweet potatoes and cook, stirring frequently, for 5 minutes. Add seasonings, from the chili powder to the red pepper flakes, if using, and cook for 1 minute. Add the tomatoes with their juice and the chicken broth. Bring mixture to a simmer, cover the pan, and cook for 10 minutes, stirring occasionally. Meanwhile, rinse and drain the beans. Set aside.
3. Remove the cover, stir in the beans and simmer mixture until the potatoes are completely tender and the chili has thickened, about 20 minutes. Season, to taste, with salt and pepper. Serve chili in bowls and allow each person to choose their own garnishes from the chili bar.