1. Heat olive oil in a skillet over medium-high heat. Brown the beef in batches, then transfer to the slow cooker.
2. In the same skillet, add garlic and tomato paste. Cook for 1-2 minutes, then add red wine. Bring to a boil, scraping up any browned bits from the bottom of the skillet.
3. Pour the wine mixture into the slow cooker. Add beef broth, carrots, onions, thyme, salt, and pepper. Stir to combine.
4. Cover and cook on low for 8 hours, or until the beef is tender.
5. About 30 minutes before serving, add the mushrooms to the slow cooker. Stir and continue to cook until the mushrooms are tender.
6. Serve hot, garnished with fresh parsley if desired.