Heat a large pot or Dutch oven over medium-high heat. Add the Italian sausage and cook, breaking up the meat into smaller pieces, until just cooked through and no longer pink, about 5 minutes. Drain off excess fat and return to the pot.
Add the fennel and onion and continue to cook, stirring, until the fennel is tender, about 4 minutes.
Pour in the white wine and cook, stirring, until reduced by half, about 2 minutes.
Add the broth, fire-roasted tomatoes, cannellini beans (drained!), parmesan cheese rind (if using), salt, pepper, and Italian seasoning. Bring to a rapid simmer.
Once simmering, reduce the heat to a light simmer, cover and cook until the flavors have melded and the beans are tender, about 15 minutes.
Discard the parmesan cheese rind and add the lemon zest, lemon juice, and kale to the soup. Stir to combine and cook until the kale has wilted, about 4 minutes. Taste and add salt as needed.
To serve, ladle soup into bowls and top with the grated parmesan, a sprinkle of red pepper flakes, and a few cracks of black pepper, if desired.