Heat a medium pan or skillet over medium heat. Add the olive oil and onion and cook for 2-3 minutes, until just beginning to soften, stirring occasionally.
Add the sausage, breaking apart with a spoon. Cook until the sausage is browned and cooked through, stirring occasionally, about 3-5 minutes. Drain any excess fat if desired.
To the same pan, add the garlic, Italian seasoning, and tomato paste. Cook for 1 minute, stirring constantly.
Transfer the sausage-tomato paste mixture to a 6-quart slow cooker. Add the crushed tomatoes, carrot, stock, and salt, stirring to combine.
Cover and cook on high for 3-4 hours on high, or low for 5-6, or until the carrots are tender.
Uncover, switch to high (if not set to high already) and add the tortellini, stirring to combine. Cover and cook an additional 5-15 minutes on high, or until the tortellini is cooked through. Time will vary depending on your slow cooker, so check on the low end of time, then add time in increments of 5 until they reach the desired doneness.
Uncover and add the spinach, cream, and red wine vinegar, stirring to combine. Taste and add salt or additional vinegar if desired.