Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Add the Italian sausage, breaking it up with a spoon, and cook until browned and cooked through, about 5-7 minutes. Drain off any excess fat, leaving about 1 tablespoon in the pot.

Reduce heat to medium. Add chopped onion, carrots, and celery to the pot. Sauté for 5-7 minutes, until the vegetables begin to soften. Stir in the minced garlic and cook for another 1 minute until fragrant.

Stir in the tomato paste and cook for 1-2 minutes, stirring constantly, to deepen its flavor. Pour in the diced tomatoes (undrained) and broth. Add the bay leaf, dried oregano, and red pepper flakes (if using). Bring the soup to a simmer.

Once simmering, reduce the heat to low, cover, and let the soup gently cook for 20 minutes to allow the flavors to meld.

After 20 minutes, stir in the diced zucchini, green beans, and rinsed cannellini beans. Continue to simmer, uncovered, for another 10-15 minutes, or until the vegetables are tender-crisp.

Add the small pasta to the pot and cook according to package directions, usually 7-10 minutes, or until al dente. Ensure the soup has enough liquid; if it seems too thick, add a splash more broth or water.

Remove the bay leaf. Stir in the fresh spinach and cook just until wilted, about 1-2 minutes. Taste and adjust seasoning with salt and freshly ground black pepper as needed.

Ladle the hot minestrone soup into bowls. Garnish generously with fresh chopped parsley and a sprinkle of grated Parmesan cheese. Serve immediately with crusty bread.