Cook noodles according to package directions. Drain and set aside.
Heat oil over medium heat in a large pan. Add the garlic, ginger, broccoli and sliced peppers. Saute until very soft, 5-7 minutes.
In a medium sized bowl, whisk together the soy sauce, rice vinegar and sriracha. Pour the sauce into the pan and lower the heat.
In a small bowl, whisk together the cornstarch with 4 tsp. of water until the cornstarch is dissolved. Slowly pour the slurry into the pan sauce and whisk until combined.
Let the sauce and vegetables simmer until the sauce is thickened. Remove from heat. Stir in the noodles and sesame seeds. Garnish with scallions.