Pour the avocado oil into a Dutch oven or large pot on medium-low heat.
Add the onion, celery, and bell pepper and saute until tender, about 5-7 minutes.
Add the garlic and red pepper flakes and saute for 1-2 minutes longer.
Stir in the cannellini beans and broth. When the mixture reaches a boil, turn the heat to low, put the lid on, and simmer for at least 10 minutes. Stir occasionally. The longer you let it simmer, the thicker the soup will be.
Stir in the pesto and simmer for about five more minutes.
Sprinkle on your favorite shredded cheese and enjoy warm!
Notes
Pesto bean soup also tastes great with parmesan and mozzarella!