In a medium shallow bowl, place in the sliced onions
To a small saucepan add the apple cider vinegar and rice syrup, whisk together over medium heat until rice syrup is dissolved.
Remove the liquid from the heat and pour over sliced onions
Sprinkle in salt and coriander seeds
Mix the onions and liquid together so onions are all coated and covered
Let sit for 10-20 minutes until the onions start to soften and a pink colour starts to emerge.
Place the onions and all the liquid in a small jar, the onions will continue to pickled over time.
Store in the fridge for up 5 days