In a bowl, whisk together soy sauce, brown sugar, hoisin sauce, bourbon, water, garlic, and ginger until smooth and well combined.
Toss chicken pieces with a little salt, pepper, and cornstarch until lightly coated for better browning.
Heat vegetable oil in a large skillet over medium-high heat until hot and shimmering.
Add chicken in a single layer and sear until golden brown on all sides, about 5–7 minutes.
Pour in the prepared sauce mixture and stir well, letting it bubble and coat the chicken.
Reduce heat to medium and simmer until sauce thickens into a glossy glaze, about 7–10 minutes.
Stir occasionally and scrape the bottom of the pan to enhance flavor and prevent sticking.
Add sesame oil and optional red pepper flakes, mixing until fully combined.
Cook until chicken is fully cooked through and sauce is sticky and shiny.
Remove from heat and garnish with chopped green onions before serving.
