Mix the sauce ingredients together in a bowl. Feel free to adjust to sauce to your desired taste.
In another small bowl, mix the cornstarch and water together until the corn starch is diluted. Set sauce and slurry aside.
Boil pasta 2 minutes less than package directions, (al dente) then drain from the water. Set aside some pasta water.
Heat a pan over medium heat. Add some oil. Sauté the onions, while parts of the scallion/green onion, bell peppers, and mushrooms until cooked. Add in the garlic. Add in the sauce mix.
Allow to simmer over medium heat. Once the sauce boils, add in the al dente pasta.
Stir the corn starch slurry again to make sure the starch isn't sticking to the bottom of the bowl. Pour in the cornstarch slurry over the pasta. Mix and cook over medium heat until the sauce thickens a bit and coats the pasta.
Mix well and leave to cook for a few minutes until pasta has absorbed some of the sauce. Add in the cashews or peanuts (if using) and the green parts of the scallion/green onion. Season to taste, if needed.
Turn off the heat. Top with sliced green onions. Enjoy.