Cook the sausage in a large sauce pan over medium heat and set aside, about 8 minutes, draining any grease from the pan.
Add the oil and onion and cook until tender, about 5-7 minutes.
Add the garlic and red pepper flakes and cook until fragrant, about a minute.
Add the broth, sausage, apples, beans, oregano, bay leaf and parmesan rind, bring to a boil, reduce the heat and simmer until apples are tender, about 10-15 minutes.
Add the kale and simmer until it wilts, about 1-2 minutes.
Season with salt, pepper and lemon juice, remove from heat, remove bay leaf and parmesan rind and serve while hot.
Optional: Puree some of the apples and beans for a creamy broth.