Pickled onions go great with just simmering vinegar water salt and sugar with peppercorns, fennel seeds, some cloves and then pouring over the onions. The onions are ready almost as soon as they cool, otherwise can be kept in the fridge.
I don't think fridge pickles are really fermented either. To ferment them you have to do it a different way with sterilized jars and cover the cucumbers with brine and leave it out for a month. You can look up a recipe
