Heat the olive oil in a large skillet over medium-high heat. Add the lamb pieces and brown them on all sides for about 5 minutes. Transfer the lamb to the slow cooker.
Add the mushrooms, carrots, onion, and garlic to the slow cooker with the lamb.
In a bowl, whisk together the red wine, beef broth, tomato paste, thyme, bay leaves, salt, and pepper. Pour the mixture over the ingredients in the slow cooker.
Cover and cook on low for 8 hours until the lamb is very tender.
Remove the bay leaves before serving.