Bring a large pot of salted water to a boil. Add the cheese tortellini and cook according to package instructions, usually about 3-5 minutes. Once cooked, drain and set aside.
In a medium skillet, heat the olive oil over medium heat. Add the Italian sausage, breaking it apart with a wooden spoon. Cook until browned and cooked through, about 5-7 minutes.
Add the minced garlic to the skillet with the sausage and cook for an additional minute until fragrant.
Stir in the drained diced tomatoes, heavy cream, and Italian seasoning. Bring the mixture to a simmer, then reduce heat and let cook for about 5 minutes until slightly thickened.
Season the sauce with salt and pepper to taste, then add the cooked tortellini and stir to combine. Allow to heat through, about 2-3 minutes.
Remove from heat and stir in the grated Parmesan cheese until melted and well combined.
Serve hot, garnished with fresh basil if desired.