In a large skillet, heat oil over medium-high heat. Add sweet potatoes and onion; cook and stir until lightly browned, 5-8 minutes. Add garlic; cook 1 minute longer. Stir in chicken, black beans, zucchini, broth, salsa, red pepper and seasonings., Bring to a boil; reduce heat. Simmer, covered, until sweet potatoes are tender, 10-12 minutes. If desired, serve with sour cream and cilantro.