In a bowl, combine gochujang and rice syrup.

Add gochugaru (Korean hot pepper flakes), vinegar, and cooking oil.

Add water and mix well until the sauce is smooth. Set aside.

Trim any excess fat from the chicken thighs and cut them into 1.5 to 2-inch pieces.

Place the cut chicken in a bowl. Season with soy sauce and black pepper.

Mince the garlic and the white part of a green onion, then add them to the chicken.

Mix everything together with your hands to coat the chicken well. You can let it marinate for 30 minutes or cook right away.

Cut the remaining green onions and rice cakes into 1.5 to 2-inch pieces.

Thread the marinated chicken onto skewers, alternating with pieces of green onion or rice cake if desired. You can also make separate skewers for vegetables and rice cakes.

Preheat a grill and place the skewers on it.

Grill for about 10 minutes, turning them over occasionally, until the chicken is almost fully cooked.

Brush the spicy sauce generously over all sides of the skewers.

Continue grilling for a couple more minutes, turning frequently, until the sauce is slightly caramelized and the chicken is fully cooked.

Remove the skewers from the grill and serve hot.