In a mixing bowl, whisk together light soy sauce, dark soy sauce, rice vinegar, brown sugar, toasted sesame oil, cornstarch, and water until smooth. Set aside.

Toss cubed chicken with 1 tablespoon of the prepared sauce, cornstarch, and a pinch of salt. Marinate for about 10 minutes.

Heat peanut oil in a large skillet over medium-high heat. Add marinated chicken and cook for 5-7 minutes until golden brown. Remove and set aside.

In the same skillet, add more peanut oil, sauté minced garlic and ginger with the diced chili pepper for 30 seconds. Add sliced onion and chopped green bell pepper, stir-fry for 3-4 minutes.

Reduce heat to medium, re-whisk the sauce, pour over vegetables and add chicken. Toss together for 2-3 minutes until heated through.

Adjust seasoning with freshly ground black pepper to taste. Serve hot over steamed rice or noodles.