Heat the olive oil in a large skillet over medium-high heat. Add the lamb cubes and brown them on all sides for even color and better flavor.
Add the diced onion and minced garlic to the skillet. Cook for 2 minutes until the onion softens.
Transfer the lamb mixture to the slow cooker. Pour in the red wine and beef broth.
Stir in the tomato paste, then add the carrots, parsnips, and potatoes. Tuck in the rosemary, thyme, and bay leaves.
Season with salt and pepper. Cover and cook on low for 8 hours until the lamb is fork-tender.
Remove the herb sprigs and bay leaves before serving.