Heat vegetable oil in a large stock pot over medium high heat.
Form sausage into ½-inch meatballs. Add meatballs to the pot. You may have to work in batches so you don’t overcrowd. Cook meatballs until they are browned on all sides and no longer pink in the center, about 7-10 minutes. Remove meatballs from the pot and set aside. Drain any grease from the pot.
In the same pot, add the broth, fennel seeds, tomato sauce, diced tomatoes, and carrots. Bring the pot to a boil. Reduce heat to low, cover, and simmer until carrots are tender, about 10 minutes.
Add squash, zucchini, basil, and tortellini. Bring pot to a boil over medium high heat and cook until tortellini is tender, about six minutes. Add meatballs and heat through.
Season with salt and pepper. Garnish with Parmesan cheese if desired.