In a medium bowl, whisk together dark soy sauce, chicken broth, rice vinegar, light brown sugar, sesame oil, sriracha, water, and black pepper until fully combined. Set aside.

Combine boneless chicken thighs with dark soy sauce and cornstarch in a separate bowl. Toss to coat and marinate for at least 10 minutes.

Heat a tablespoon of oil in a skillet over medium heat. Add marinated chicken thighs in batches, cooking for about 3 minutes on each side until golden brown. Keep warm.

In the same skillet, sauté minced garlic and ginger over medium-low heat for about 1 minute until fragrant.

Return chicken to the skillet, add sliced red bell pepper and chopped green onions, then pour the prepared sauce over and simmer for 2-3 minutes until thickened.

Serve hot over steamed rice.