In a small saucepan, cook the rice according to the package instructions, adding the butter and salt.
Stir together all the sauce ingredients. Set aside.
In a medium bowl, combine the cornstarch and salt. Pat the chicken dry, cut into cubes and add to the cornstarch mixture, tossing to coat. Set aside. Prepare the vegetables.
Heat a 10-inch cast-iron skillet over medium-high heat. Once warm, add the neutral and sesame oils. Add the chicken and cook for 4 minutes, or until lightly browned but not cooked all the way through.
Lower heat to medium; add broccoli, carrots and edamame. The pan will be exceptionally full at first. Cook 5 minutes or until the vegetables are barely tender and the chicken is done, stirring frequently.
Pour the prepared sauce over the chicken and vegetables. Cook for a minute more. Taste and add more salt if necessary. Serve over the rice. Garnish with the cashews, green onions and, if desired, Sriracha.