1. Place red onion in clean and sterilised jar. In a jug, mix together water, apple cider vinegar, sugar and salt and stir until well combined and the sugar and salt are dissolved.
2. Pour the pickle over the onion in the jar. Add the fresh peeled ginger and seal for a least 2 hours or overnight. Serve with the sliders.
The pickled onions with the sweet and sour flavour are great in a variety of dishes like salads and with meat and fish.