Season the pork roast on all sides with salt, pepper, garlic powder, and thyme.
Place the sliced onions in the bottom of the slow cooker.
Place the pork roast on top of the onions.
Pour the beef broth around the sides of the roast.
Cover and cook on low for 8 hours until the meat is tender and easily shreds.
Remove the roast from the slow cooker and set aside to rest.
Strain the cooking liquids into a saucepan.
In a small bowl, whisk together cold water and cornstarch to create a slurry.
Bring the cooking liquids to a simmer over medium heat and whisk in the cornstarch slurry.
Simmer for 3 minutes until thickened and serve gravy over the sliced or shredded pork.