Cook the rice
Wash and cook your short-grain rice according to the packet instructions.
Allow the cooked rice to cool slightly before assembling the rice balls.
Cook the kimchi
Finely chop the kimchi.
Heat the sesame oil in a pan over medium heat and fry the kimchi for 2–3 minutes.
Add the light soy sauce, gochujang, sugar and oyster sauce. Mix well and cook for another 3 minutes, allowing the kimchi to caramelise slightly.
Remove from the heat and let it cool.
Make the kimchi rice
Add the cooled kimchi mixture to the cooked rice.
Add the minced spring onion, sesame seeds and a pinch of salt.
Mix everything together until evenly combined.
Shape the rice balls
You can use a heart-shaped mould, cling film or just your hands.
Take a portion of the rice mixture and flatten it against your palm.
Add a generous amount of mozzarella to the centre, then cover with more rice, making sure the cheese is completely enclosed.
Use your hands to form the rice into a ball, then gently shape it into a triangle-ish onigiri shape.
Using your thumb or finger, press an indent into the top centre of one side to create the heart shape.
Repeat with the remaining rice mixture.
Get them crispy
Brush the outside of each rice ball generously with sesame oil.
Place them in a preheated air fryer or oven at 200°C.
Cook for around 15–20 minutes, turning halfway through. Brush with a little more sesame oil after flipping.
Cook until the outside is golden and crispy and the cheese inside is beautifully melted.
Serve
Let them cool for a couple of minutes before digging in!