If using wooden skewers, soak them in water for at least 15-30 minutes.

To a large bowl, add the Gochujang paste, soy sauce, rice vinegar, brown sugar, sesame oil, salt, and pepper, and whisk to combine to create the chicken marinade. Taste, and if desired, add more of a certain ingredient.

Remove 1/3 cup of the marinade and place it in a small saucepan; set aside.

Add the diced chicken to the bowl, toss to coat evenly, and marinate for 15-30 minutes. If marinating closer to 30 minutes, cover and place the bowl in the fridge. Do NOT marinate longer than indicated; the acidity of the ingredients will break down the chicken protein fibers too much and the chicken will be mushy.

Place the saucepan with the reserved 1/3 cup marinade on the stove, heat over medium-high for about 2-3 minutes, or until the sauce reduces, thickens, and becomes sticky; stir nearly continuously so it doesn't burn. Set aside off the heat until it's time to baste the chicken.

After marinating, thread the chicken on approximately 5 to 8 skewers, depending on how much chicken you're using and the exact length of your skewers. Don't compress or overly compact/squish the chicken onto a skewer. If you're running out of space, start a new skewer. If adding red pepper, alternate chicken and red pepper chunks on skewers.

When ready to cook, discard the marinade that was in the marinating bowl.

For grilling (outdoors): Oil the grill grates, and preheat outdoor gas grill to medium-high heat. Place the skewers on the grill, close the lid, and grill for approximately 3-4 minutes, open the lid, flip the chicken using tongs, baste it generously with the sauce that you reduced, and cook for another 2-4 minutes, or until the chicken is done (160F internal temperature, resting to 165F); baste as much as desired for juicier chicken with richer flavor.

For grill pan (indoors on stove): Preheat a grill pan over medium-high to high heat on your stove, place the skewers on top, and cook for approximately 5 minutes, flip the chicken using tongs, baste generously, and cook for another 3-5 minutes, or until the chicken is done (160F internal temperature, resting to 165F); baste as often as desired for juicier more flavorful chicken.

For oven baking: Preheat oven to 400F and place a grill rack over a parchment-lined baking sheet, and arrange the skewers on the prepared rack. Bake in the preheated oven for about 20 minutes, or until the chicken is cooked through and lightly charred on the edges. Flip midway through baking with tongs, baste generously, and you can even flip and baste another time before chicken is fully done for juicier, moister chicken.

Optionally garnish with green onions, sesame seeds, fresh herbs such as basil or cilantro, or as desired. Serve the chicken right on the skewers, or remove it from the skewers and serve it alongside rice, over a salad, or as desired.