Heat a skillet over medium heat and brown the beef cubes on all sides. Transfer the beef to the slow cooker.
Add the rinsed lentils, sliced carrots, cubed potatoes, sliced parsnip, diced onion, and minced garlic to the slow cooker.
Pour in the beef broth and stir in the dried thyme, bay leaves, salt, and pepper.
Cover and cook on low for 7 to 8 hours until the beef is tender and the lentils are soft.
Remove the bay leaves before serving.