In a large pot over medium heat, add the oil and sausage (if using). Cook until the sausage is browned and cooked through. Transfer to a plate and set aside.
Add the onion, carrot, celery, garlic, and ½ teaspoon salt and cook for 5 minutes, stirring occasionally.
Stir in the tomato paste, oregano, and fennel and stir constantly for about 30-60 seconds. Add the water, parm rind (if using), and remaining 1 teaspoon salt. Bring to a boil, then reduce to low and simmer for 10 minutes. Add the tortellini and cook according to the package instructions. When there is just 1 minute left, stir in the spinach and peas. Make sure the water comes back to a boil for a whole minute to finish cooking. Stir in the sausage (or top your bowls with sausage, if using).
Serve topped with plenty of parmesan, parsley, and a drizzle of your best olive oil.