Boil a pot of water. Once boiling, add the rice cakes and let them soak for 30 seconds, or until rice cakes turn soft. Strain the rice cakes using a colander and set aside. Once the rice cakes are no longer hot, skewer 2-3 rice cakes in one skewer. You can skip this step if you're using fresh and soft rice cakes.
Meanwhile, heat the sauce in a separate saucepan briefly for 30 seconds to dissolve the sugar. Keep stirring so it doesn't burn.
Add oil to a heated griller. Place skewered rice cakes on a grill and cook for 1-3 minutes on each side, or until they turn golden brown. Remove from the grill and brush the sauce over. Garnish with sesame seeds and green onion. Serve immediately.