Heat olive oil in a large pot over medium heat.
Add onion, garlic and red pepper flakes and cook until fragrant (about 2 minutes).
Add celery and saute for 2 minutes.
Add diced tomatoes (with juice) and continue cooking for an additional 2 minutes.
Add vegetable broth, butternut squash, salt, and pepper and simmer until butternut squash is fork tender (about 15 minutes).
Add white beans and kale or spinach and stir to wilt.
Optional: Serve with toasted bread and garnish with parmesan cheese except during phase 2-3.