In a large pot of boiling water, cook ramen noodles until tender, about 3-4 minutes; rinse with cold water and drain well.
In a medium bowl, whisk together beef stock, oyster sauce, rice wine vinegar and Sriracha.
Heat sesame oil in a large skillet over medium heat. Add ground beef and onion, and cook until beef has browned, about 3-5 minutes, making sure to crumble the beef as it cooks; drain excess fat.
Stir in garlic and ginger until fragrant, about 1 minute.
Stir in beef stock mixture, scraping any browned bits from the bottom of the skillet.
Stir in ramen noodles until heated through and evenly coated in sauce, about 1-2 minutes.
Serve immediately, garnished with green onions and sesame seeds, if desired.