Whisk together beef broth, soy sauce, brown sugar, cornstarch, ginger, garlic, and rice vinegar in a bowl until the mixture is combined.

Heat 2 tablespoons of canola oil in a large skillet over medium-high heat. Add onion and cook, stirring occasionally, until softened, about 2 minutes. Add broccoli and cook until bright green and tender-crisp, approximately 6 to 7 minutes. Transfer to a plate.

Reduce heat to medium and add the remaining tablespoon of oil to the skillet. Add ground beef and salt, cooking while stirring to break meat into crumbles until browned, about 5 minutes.

Whisk the prepared sauce mixture again and pour it into the skillet. Cook over medium heat, stirring constantly, until the sauce thickens slightly, approximately 3 to 5 minutes.