Add the carrots, potatoes, and parsnips to the bottom of the slow cooker.
Place the pork loin roast on top of the vegetables.
Sprinkle the minced garlic, rosemary, thyme, salt, and pepper over the pork.
Pour the chicken broth and the juice of both lemons into the slow cooker around the pork.
Scatter the lemon zest over the top of the pork.
Cover and cook on low for 7 to 8 hours until the pork reaches an internal temperature of 145°F and the vegetables are tender.
Slice the pork and serve it with the vegetables and some of the cooking liquid spooned over the top.