Slice onions then add to a clean 24 oz mason jar.
Add vinegar honey (if using) and salt.
Heat water in a pan over stove or in a kettle until boiling. Pour the boiling water over the onions, ensuring they are fully submerged.
Put the lid on the jar and give it a little shake to ensure everything is well combined.
Let sit for an hour on the counter before putting in the fridge.