Heat the vinegars, coconut sugar, salt and allspice in a saucepan. Bring to a full boil then immediately move from heat. Pour the vinegar mixture over the onions and allow them to sit until cooled to room temperature, stirring every 10 to 20 minutes.
Transfer the onions and liquid to a sealable jar and refrigerate overnight. Onions are ready when soft and flavorful. Onions will keep in the refrigerator for up to 1 month in a sealed container.
Notes
You can use regular cane sugar in place of coconut sugar.