In a large mixing bowl, combine the cubed chicken breasts and buttermilk. Make sure the chicken is well-coated. Cover the bowl with plastic wrap and let it marinate in the refrigerator for at least 1 hour, or overnight if you have the time.
While the chicken is marinating, preheat your oven to 400°F (200°C). In another bowl, mix the finely crushed corn flakes, flour, and black pepper.
Once the chicken has marinated, remove it from the refrigerator. Take each piece of chicken and dip it into the cornflake mixture, ensuring each piece is thoroughly coated. Place the coated chicken on a baking sheet lined with parchment paper or a wire rack.
Lightly brush the tops of the coated chicken pieces with extra virgin olive oil.
Place the baking sheet in the preheated oven and bake for 20-25 minutes, flipping the chicken halfway through. The chicken is done when it reaches an internal temperature of 165°F (74°C).
While the chicken is baking, make the sauce by combining the soy sauce, honey, Gochujang, rice vinegar, grated ginger, grated garlic, and toasted sesame oil in a small saucepan over medium heat until it simmers.
Once the chicken is done baking, transfer it to a large serving platter. Drizzle the sauce over the chicken, sprinkle with toasted sesame seeds and chopped green onions, and serve immediately.
