Place the frozen tteok in a pan in a single layer. Add green onions in between the rice cakes.
Drizzle with oil and toast over high heat until the bottom starts to crisp.
While that cooks, mix the sauce: 4 parts sugar, 3 parts sesame oil, 3 parts ketchup, and 2 parts gochujang. Stir until smooth.
In a small bowl, mix a little water with potato starch to make a slurry.
Once the tteok is crisping, pour in the slurry so the rice cakes bind together like a pancake.
Use a plate to carefully flip it over.
Toast the other side until golden and crispy.
Spread the sauce over the top like a pizza and let it cook for a moment so it clings to the surface.
Serve hot while it's crispy outside and chewy inside.
