Heat oil in a large skillet over medium-high heat. Add onion and ground turkey, cooking until the onion is translucent and the turkey is cooked through, breaking up the turkey as you go. Add garlic and cook just until fragrant, about 30 seconds.
Transfer the mixture to your BLACK+DECKERĀ® slow cooker. Stir in pasta sauce and Italian seasoning. Cook on low for 6 hours or low for 3 hours. Add tortellini and mozzarella cheese; cook another 30 minutes, until the cheese is melted and the tortellini warmed through. Top with Parmesan cheese before serving.