In a large sauté pan, add the olive oil and place over medium heat. Add the onions and saute for about 3 minutes till fragrant. Add the sausage and continue cooking for about 2 minutes. Add the garlic and cook for an additional 30 seconds. Remove from the heat.
In a 6 qt. slow cooker add the sausage-onion mixture, tomatoes, tomato paste, stock, basil, oregano, salt and pepper. Cover with a lid and cook on high for about 3 1/2-4 hours.
Add the tortellini and cook for an additional 20 minutes.
Once the tortellini is cooked, add the chopped kale, heavy cream and parmesan and cook for an additional 10 minutes. Adjust the seasoning as needed and serve hot.