Put the strips of steak in a bowl. Mix together the garlic, sesame oil, soy sauce and mirin and pour over the beef. Leave to marinate in the fridge for a minimum of half an hour.
Add the rapeseed oil to a wok or large frying pan and heat over a medium high heat. Add the beef and fry for 2 minutes, tossing frequently, before adding the chilli, spring onions, cucumber and pak choi. Continue to stir-fry for a further 3 minutes. Squeeze over the juice of 1 lime and toss through the fresh coriander.
Meanwhile, cook the rice according to the instructions on the packet. Divide between 4 bowls, then top with the beef. Scatter over the sesame seeds.