Cut the rice cakes and chicken into bite-size pieces.
Slice the onion and green onion thinly.
Add cooking oil to a pan and stir-fry the chicken first.
When the chicken is halfway cooked, add the rice cakes and vegetables and stir-fry together.
Add gochujang (Korean chili paste), soy sauce, and sugar; stir-fry until the seasoning is well absorbed.
Top with mozzarella cheese and cook on low heat until the cheese melts.