In a medium bowl, combine the ground beef with the 1/4 finely chopped onion, garlic, Worcestershire sauce, salt, and pepper.
Cover the bowl and refrigerate for 20-30 minutes.
In a large skillet, drizzle 1 tablespoon (15 milliliters) of the vegetable oil over medium low heat.
Add the remaining 3/4 chopped onion and cook, stirring occasionally, until beginning to caramelize, 20-30 minutes. Adjust between medium low to low to keep the onions from burning.
Pour in the beef stock and season with the soy sauce and worcestershire sauce. Bring the mixture to a simmer.
In a small bowl, whisk together the cornstarch and water. Pour into the simmering stock and stir to combine. Continue to simmer, stirring often, until the mixture has thickened.
Remove from heat. Adjust seasonings as desired.
In another large skillet, drizzle the remaining 1 tablespoon (15 milliliters) vegetable oil over medium heat.
Crumble in the ground beef mixture and cook, stirring occasionally, until browned.
Add the mushrooms and cook, stirring occasionally, until softened and the moisture has evaporated.
Remove from heat and allow to cool slightly.