Set a large pot of water to boil. Add ramen noodles and cook 'til tender, about 3-4 minutes. Drain well and rinse with cold water; set aside.
In a medium bowl, whisk beef stock, oyster sauce, rice wine vinegar and Sriracha until well blended.
In a large skillet over medium heat, add sesame oil. Add ground beef and onion. Cook for 3-5 minutes, crumbling beef as it cooks, until beef is browned. Drain excess fat.
Stir in garlic and ginger. Cook until fragrant, about 1 minute.
Add beef stock mixture. Stir well, scraping up browned bits from bottom of skillet.
Stir in ramen noodles. Cook until heated through and evenly coated in sauce, about 1-2 minutes.
Spoon into individual serving bowls. Garnish with green onions and sesame seeds, if desired.