Prepare the noodles according to package directions. If they’re fresh or refrigerated yakisoba, you can usually just loosen them up under hot water. Drain and set aside.
Make the sauce by whisking all sauce ingredients together in a small bowl. Taste and adjust if needed, add more soy sauce for salt, ketchup for sweetness, or chili flakes for heat.
Heat oil in a large skillet or wok over medium-high heat. Add the onion and red bell pepper and sauté for about 3–4 minutes until they begin to soften.
Add the corn and peas and cook for another 2–3 minutes until heated through.
Add the noodles and sauce to the skillet. Use tongs to toss everything together until the noodles are coated and everything is warmed through. This should only take a few minutes.
Top with green onions if you’re using them and serve hot!
