In a medium-sized bowl, prepare the marinade by whisking together soy sauce, balsamic vinegar, sesame oil, and cornstarch. Add the chicken and stir to coat. Let stand at room temperature for about 15 minutes.
In another bowl, prepare the sauce by whisking together the soy sauce, dark soy sauce, hoisin sauce, balsamic vinegar, sesame oil, sugar, and cornstarch. Set aside.
In a wok (or large skillet) over medium heat, add the peanut oil. Stir in the crushed red pepper flakes. Add the red and green bell peppers. Cook for 3-4 minutes or until the peppers are slightly softened. Stir in the minced garlic and ginger. Cook for an additional minute. Add the chicken with a slotted spoon (no need to include extra marinade). Cook the chicken for 4-5 minutes or until it's thoroughly cooked.
Add the sauce to the chicken and mix it to coat the chicken. Stir in the peanuts and cook for an additional 1-2 minutes. Remove from heat and toss in half of the chopped green onions. Transfer to a serving plate; sprinkle the top with the remaining green onions. Serve with white rice.