In a small mixing bowl, add the minced garlic, rosemary, thyme, paprika, salt, and pepper, mix until well combined. Add the olive oil and mix to form a paste. Rub the garlic mixture all over the boneless leg of lamb.
Heat a large skillet over medium-high heat and sear the leg of lamb and all sides for about 2-3 minutes per side until browned. Once browned on all sides, set aside.
To the slow cooker, add the shallots, carrots, and celery. Place the seared leg of lamb over the vegetables.
Pour the chicken or beef broth around the leg of lamb, the liquid should reach about halfway up the lamb.
Cover the slow cooker and cook the lamb on low heat for 6-8 hours, or until the meat is tender and easily pulls apart with a fork.
Once the lamb is cooked, remove it from the slow cooker and allow it to rest for a few minutes before slicing. Serve the lamb with the vegetables and the cooking juices. Add additional salt and pepper if desired. Enjoy!