In a large saucepan, heat the olive oil over medium heat. Add the onion and garlic and sprinkle with salt. Cook for about 5 minutes, or until the onion is softened and translucent, stirring occasionally to prevent the garlic from burning.Stir in the sweet potato and cook, stirring frequently, for 5 to 7 minutes, or until the sweet potato is slightly softened.Add the bell pepper, jalapeno, and zucchini and saute for 5 minutes more, stirring occasionally.Add the black pepper, cumin, chili powder, cayenne pepper, and ground coriander, stir, and cook for about 1 minute, until fragrant.Add the corn, tomatoes, and vegetable broth, and stir. Bring to a boil, then reduce to medium heat. Simmer the soup, covered, for about 20 minutes, or until the sweet potato is cooked through.Uncover the soup, stir in the black beans, and simmer for 2 minutes more. Stir in the freshly-squeezed lime juice. Season to taste with additional salt, pepper, lime juice, and cayenne pepper. Serve hot, topped with garnishes of choice.