In a medium saucepan, cover sausage links with water and bring to a boil over high heat. Lower heat and keep at a simmer until the sausage is cooked through, about 15 minutes.
Drain and let the sausage cool enough to handle. Chop the sausage into bite-sized pieces.
Heat olive oil in a large pot over medium heat.
Add onion and salt and saute for 8-10 minutes, or until soft and golden. Add garlic and yellow squash. Saute for 10 minutes.
Add potatoes, chicken broth, bay leaves, and 1 can of drained, rinsed butter beans. Simmer soup for 20 minutes.
Add chopped sausage, green beans, the second can of butter beans, and pesto sauce.
Simmer the soup for 5 minutes.
If you wish, serve soup with an extra dollop of pesto in the bowl.