Cut the beef and kimchi into bite-sized pieces.
Slice the onion and green onion.
Heat cooking oil in a pan and stir-fry the green onion to bring out its aroma.
Add the beef and stir-fry.
Add the kimchi and stir-fry together.
Add the onion and stir-fry.
Season with soy sauce, sugar, and chili powder.
Stir-fry until all the ingredients are cooked through.
Finish by drizzling with sesame oil and sprinkling sesame seeds.