Sprinkle beef with baking soda. Marinate 15 minutes.
While beef is marinating, prepare sauce by whisking together peanut butter, soy sauce, brown sugar & sriracha. Set aside.
After 15 minutes, rinse beef thoroughly under cold water to remove all baking soda. Pat dry.
Heat oil in a large skillet or wok, over medium high heat. Add beef. Stir fry 7-10 minutes until beef is nicely browned and cooked through.
Add sauce and stir. Add vegetables and stir to coat everything evenly, cooking 1-2 more minutes.
Just before serving, top with chopped peanuts.
Serve over rice or noodles.