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 chicken stock, oyster sauce, rice wine vinegar and Sriracha.
Heat canola oil in a large skillet over medium heat. Add chicken and cook until golden and cooked through, about 4-6 minutes; set aside.
Stir in broccoli, onion, bell pepper and mushrooms until tender, about 4-5 minutes.
Stir in garlic and ginger until fragrant, about 1 minute.
Stir in chicken stock mixture, scraping any browned bits from the bottom of the skillet.
Stir in ramen noodles and chicken until heated through and evenly coated in sauce, about 1-2 minutes.
Serve immediately, garnished with green onions and sesame seeds, if desired.