In a large bowl, mix ground beef, Worcestershire sauce, seasoning salt, garlic powder, and black pepper. Shape into thick, round patties (about 1 inch thick), smoothing the edges.
Heat a pan over medium heat and cook patties for 3–5 minutes on each side, or until fully cooked. Set cooked patties on a paper towel-lined plate to drain excess grease.
In the same pan, melt 1 tbsp butter and sauté onions for 1 minute, then add mushrooms for another 1–2 minutes.
Whisk together beef stock, shoyu, Worcestershire sauce, ketchup, and cornstarch until smooth. Stir until it thickens and starts to simmer.
Melt a little butter in a pan, crack in the egg, and cook sunny-side up (or to your preference). Set aside.
Scoop hot rice onto a plate, add a hamburger patty, pour over the gravy, and top with the egg.