Pat chicken breasts completely dry with paper towels. If breasts are uneven in thickness, pound between plastic wrap to uniform 3/4-inch thickness. Season both sides with salt and pepper.
In a small bowl, combine soy sauce, honey, minced garlic, rice vinegar, grated ginger, sesame oil, and red pepper flakes (if using). Whisk until honey is fully integrated. Reserve 2 tablespoons of the mixture for final glazing.
Heat your skillet over medium-high heat until hot but not smoking. Add oil and swirl to coat the surface.
Place chicken breasts presentation side down in the hot skillet. Do not move them for 3-4 minutes until a golden-brown crust forms.
Flip chicken breasts, reduce heat to medium-low, and pour half of the sauce (excluding the reserved portion) over the chicken. Cover with lid.
Continue cooking covered for 7-9 minutes, or until internal temperature reaches 160°F (71°C) at the thickest part.
Remove lid, increase heat to medium, and add remaining non-reserved sauce. Cook uncovered for 1-2 minutes, occasionally spooning sauce over chicken as it thickens.
Transfer chicken to a cutting board and let rest for 5 minutes. During the rest, brush with reserved sauce for final flavor enhancement.
Slice chicken against the grain at a slight diagonal. Drizzle with any remaining glaze from the skillet, then garnish with sliced green onions, sesame seeds, and optional cilantro.