Season the chuck roast generously with salt and pepper on all sides.
Place the quartered onion and minced garlic in the bottom of your slow cooker.
Set the roast on top of the onions and spread tomato paste over the top of the meat.
Pour beef broth around the roast until it comes halfway up the sides, then add thyme and bay leaves.
Cover and cook on low for 8 hours or high for 5 hours until the meat is fork-tender.
Remove bay leaves, then slice or shred the roast and serve with the cooking liquid as gravy.