Before you start, bring a full kettle to the boil.
Combine rice, boiling water measure and a pinch of salt in a medium pot and bring to the boil with the lid on. Once boiling, reduce to lowest heat to cook for 12 minutes. Turn off heat and steam, covered, for 5 more minutes. Do not lift lid during cooking.
Prep cucumber, bok choy and radish. Combine with chilli flakes, vinegar and soy sauce in a medium bowl. Season with salt. Set aside.
Prep spring onion and mix in a large bowl with remaining meatball ingredients (except oil and gochujang sauce), until well combined. Roll into golf ball-sized balls.
Heat oil in a large fry-pan on medium-high heat. Cook meatballs for 10-15 minutes, until browned and cooked through. Add first measure of gochujang sauce to pan and toss to coat meatballs. Season with pepper.
In a small bowl, mix second measure of gochujang sauce with mayonnaise.
Serve rice topped with meatballs and gochujang mayo. Serve kimchi on the side.