Place sausage, carrots, celery, onion, tomatoes, garlic, parmesan rind, white beans, kidney beans, broth, oregano, parsley, pepper, and red pepper flake into a slow cooker. Cook on low for 6 hours.
When 30 minutes of cook time remains, add pasta and zucchini.
Stir in spinach. Serve topped with basil and grated parmesan.
Recipe by Rachel Schultz at https://rachelschultz.com/2019/07/18/sausage-minestrone/