Cook the tortellini in salted, boiling water for half the time according to the package directions (approximately 2 minutes). Drain in a colander and set aside.
Heat a 4 qt. soup or saucepan and add a tablespoon of olive oil. Add the sausage and sage. Cook until no longer pink about 8 minutes, crumbling while cooking with a spatula or wooden spoon. Remove from pan to a paper towel-lined plate and set aside.
In the same skillet, add the remaining tablespoon of olive oil and add the chopped onion. Saute for about 5 minutes until lightly golden. Add the garlic at the end and saute for 30 seconds until fragrant.
Add the tomato paste to the soup pan and swirl around in the pan until caramelized about 1-2 minutes.
To the soup pan, add the turkey stock. Stir the soup and allow it to come to a very low boil, cooking for 15 minutes total.
Add turkey, reserved sausage, tortellini and spinach to the soup during the last 2-3 minutes of cooking. Stir until the spinach has wilted and the tortellini is cooked. Taste for seasoning adding the additional teaspoon of salt if needed.
Squeeze the lemon into the soup (minus the seeds!). Serve with freshly grated Parmesan cheese.