Heat the oil in a heavy medium pot or large saucepan over medium heat. Add the onion and rosemary and sauté until the onion starts of soften, about 5 minutes. Add the squash and sauté until heated through, about 5 minutes. Add the broth and beans and bring to a boil. Reduce the heat and simmer 10 minutes to blend the flavors.
Meanwhile, cut the leftover chicken into bite-sized pieces.
Add the chicken along with its sauce and vegetables to the soup and simmer 10 longer minutes to blend the flavors.
Cut the polenta into ½-inch pieces. Add to the soup and simmer just until heated through. Divide the soup among 2 heated bowls and serve.