In a medium bowl, whisk together the chopped onion, soy sauce, brown sugar, minced garlic, sesame oil, sesame seeds, cayenne pepper, salt, and black pepper until smooth.
Add the chicken strips to the marinade and toss until evenly coated.
Heat a large skillet over medium-high heat.
Add the chicken along with the marinade to the skillet.
Cook, stirring frequently, for about 15 minutes, or until the chicken is fully cooked and the sauce has thickened slightly.
Serve the Skillet Chicken Bulgogi Recipe immediately over steamed rice or alongside your favorite vegetables.
Garnish with extra sesame seeds and sliced green onions if desired.