Combine the ground beef with salt, pepper, onion powder, and garlic powder. Make four evenly shaped patties about ½-inch thick.
Heat the vegetable oil in a frying pan over MEDIUM heat and cook the hamburger patties for about 5-minutes. Flip, and cook for another 5-minutes. Remove the hamburger steaks from the pan and place on a plate; remove the pan, as well - the gravy comes out better with a new pan and without all of the fattie residue from the hamburgers.
Melt the butter in a large clean pan; add the thinly sliced onions to the pan and cook for 10 minutes, or until the onions have softened and caramelized. Add the all-purpose flour to the pan and mix to coat the onions in it.
Slowly pour the beef broth into the pan and continue to stir as the broth thickens into a gravy. Season with salt and pepper. Simmer on MEDIUM-LOW for about 5-minutes. If the gravy becomes too thick, slowly add small amounts of broth to thin out.
Turn heat to LOW, return the hamburger steaks to the pan, cover, and simmer on LOW for 15-minutes.
Place mashed potatoes on plate and top with Hamburger Steak and Smothered Onions. Garnish with fresh parsley and chopped green onions.