In a medium saucepan over medium heat, sauté onion in half of broth until translucent. Add zucchini, collards, bell pepper, tomatoes, tomato paste, and remaining broth, and sauté for another 2-3 minutes. Add garlic, lime juice, three quarters of the cilantro, chopped (leave remaining leaves whole), salt, chili powder, and cumin. Quickly bring to a boil, then reduce to a simmer and stir occasionally for 15 minutes. Stir in beans to heat through. Just before serving garnish with cilantro and avocado.
Recipe courtesy of New York Times best-selling author and registered dietitian, Cynthia Sass.