Heat the olive oil in a skillet over medium-low heat. Once the oil is glistening, onion and cook until translucent. Add the garlic and cook until fragrant, about 30 seconds.
Add onions, garlic, sausage, beans, thyme, salt, pepper, beef bouillon to slow cooker. Cook on high for 5 hours.
Remove ⅓ of the beans. Mash in a bowl and return to slow cooker.
Add the kale and stir until the sauce becomes creamy and the kale has wilted, about 2 more minutes.
Stir in the Parmesan and lemon juice. Adjust the seasoning to taste.
Serve with extra Parmesan and red pepper flakes, if desired, and crusty bread alongside.
