Soak the rice cakes in warm water for about 30 minutes to soften them. Drain and set aside.
In a large skillet, heat the vegetable oil over medium heat. Add the minced garlic and sauté for about 30 seconds until fragrant.
Stir in the gochujang, soy sauce, sugar, and sesame oil. Mix well to combine.
Add the water to the skillet and bring the mixture to a simmer.
Add the soaked rice cakes to the skillet and cook for about 10-15 minutes, stirring occasionally, until the sauce thickens and the rice cakes are heated through.
Stir in the chopped green onion and cook for an additional minute.
Serve hot, garnished with sesame seeds if desired.