Add beef, diced onions, garlic powder, salt, pepper, soy sauce, and breadcrumbs to a bowl. Use your hands to mix until well combined (don't overmix) then divide and form into 4 patties.
Add oil to a hot pan and cook the patties on medium heat until fully cooked on both sides (about 5 minutes on each side). Remove the patties from the pan and set aside.
MAKE THE GRAVY
To the same pan where you cooked the patties, add sliced onions and mushrooms to the pan and cook until the onions turn golden and caramelized.
While the onions and mushroom are cooking, grab a small bowl and combine the beef broth, soy sauce, Worcestershire sauce, ketchup, corn starch, salt, and pepper. Whisk well and set aside.
Add butter into the pan until melted into the onions and mushroom.
Slowly pour in the stock and let simmer under low heat until the sauce thickens (about 3 to 5 minutes).
ADD PATTIES INTO THE GRAVY
Transfer the cooked patties into the pan with the gravy and let simmer for about 2 minutes.
COOK THE EGGS
Add oil to a hot pan and cook the eggs sunny side up.
ASSEMBLE THE LOCO MOCO
Add rice to each individual plate and place the beef patty over it. Drizzle a generous scoop of the gravy over the patty then top with an egg. Garnish with sliced green onions* (optional). Serve immediately.