In a large pot, heat olive oil over medium heat. Add Italian sausage, breaking it up with a wooden spoon. Cook until browned, about 7-10 minutes. Remove from pot.

In the same pot, add diced onion, chopped carrots, and chopped celery. Sauté for 5-7 minutes until softened and translucent.

Stir in minced garlic, dried oregano, dried thyme, and red pepper flakes. Cook for 1 minute until garlic is golden.

Pour in chicken broth and add back the sausage, cannellini beans, kidney beans, and diced tomatoes. Bring to a boil, then reduce heat to low and simmer for 30-60 minutes.

About 10 minutes before serving, stir in chopped kale or spinach. Cook for 2-3 minutes until wilted.

Taste and adjust seasoning with salt and pepper as needed.

Ladle soup into bowls, garnish with grated Parmesan cheese if desired, and serve with crusty bread.