Use your hands to combine the beef, breadcrumbs, broth, eggs, Worcestershire sauce, garlic powder, onion powder, salt, and pepper in a large bowl.

Layer the bottom of the slow cooker with the onion slices.

Form the beef mixture into an oval loaf shape to fit your slow cooker, leaving an inch or so of room on each side. Place the loaf on top of the sliced onion layer.

Whisk the ketchup, brown sugar, apple cider vinegar, and yellow mustard in a small bowl. Set aside about ¼ of the glaze and refrigerate it until the meatloaf is ready to serve.

Spoon the remaining ¾ of the glaze over the top of the meatloaf and spread it into an even layer coating the top and sides.

Cook the meatloaf on low for about 6 hours or on high for about 4 hours.

Remove the meatloaf from the slow cooker and cut it into slices. You can discard the onions and liquid in the slow cooker.