Cook dry noodles in salted water as per the package directions. Make sure to cook the noodles al dente. If they are overcooked, the final dish will become soggy.
Stir together soy sauce, teriyaki sauce, brown sugar, and mirin in a bowl and set aside.
Heat butter and sesame oil in a pan over high heat.
Once they are hot, add onions, minced ginger, and minced garlic and saute for 2-3 minutes until they are lightly browned.
Now add the sauce mixture and cooked noodles to the pan and toss to coat the noodles with the sauce.
Add salt and ground pepper and toss well.
Check for salt and add more if required. Sprinkle sesame seeds on top and serve immediately.