Finely slice onion and place in a microwave-safe dish with 1 tsp rapeseed oil.
Mix well to coat the onions in oil and spread out evenly on the plate
Microwave on high for 5 minutes.
Stir well, then microwave in 1-minute increments until lightly browned, stirring well each time and then reducing to 30-second increments until they are brown and a bit crispy. Then leave to cool. They will crisp up even more as they cool down
Be careful as they can go very quickly from brown to burnt so don't over do it! Also all microwaves are different so you might need a little bit longer for yours. Just keep doing 30 second bursts and mixing well in between.
