In a slow cooker, place the sliced onion on the bottom.
Arrange the cubed steak on top of the onions.
In a small bowl, whisk together the beef broth, Worcestershire sauce, soy sauce, garlic powder, black pepper, and salt.
Pour the liquid mixture over the cubed steak.
Cover and cook on low for 4-6 hours, or on high for 2-3 hours, until the steak is tender.
For gravy: Remove the steak and onions from the slow cooker, setting them aside. In a small bowl, whisk together the flour and water to create a slurry.
Pour the slurry into the liquid remaining in the slow cooker. Stir well and cook on high for about 15-20 minutes, or until thickened.
Return the steak and onions to the slow cooker and stir to coat with the gravy.
Serve hot, usually with mashed potatoes.
Notes
This recipe is very forgiving. Adjust the seasonings to your preference. For an even richer gravy, you can thicken it with a cornstarch slurry instead of flour.