Heat the olive oil over medium heat in a large skillet with a lid or a Dutch oven. Add the onion and bell pepper, and sauté until softened, about 2 minutes. Add the ground turkey and cook until the turkey is mostly browned (a little pink in the center is fine), breaking it up as you go. Add the spices (chili powder, cumin, salt and pepper), and cook and stir for another 30 seconds or until fragrant. Add the chopped sweet potato, black beans, tomatoes with juice, and chicken broth. Stir well, bring to a simmer, and then cover and reduce the heat to maintain a gentle simmer. Cook for approximately 20 minutes or until the sweet potato is tender, stirring several times.