I'm a huge fan of mexican pickled onions. I can eat them on just about anything or just by themselves. It's so easy and ready in a snap. Keep a jar of them in your fridge to liven up any salad or meal.
Slice your red onion to whatever thickness you desire, but I recommend on the thinner side. Cut too thick the head from the boiling vinegar will not par-boil the onions leaving them completely raw in the center. Thinly sliced onions will work the best.
Pack the onions into a mason jar or shallow sealable bowl.
Place all the remaining ingredients into a pot and bring to a boil. Stir to help the salt dissolve into the vinegar.
Pour the boiling liquid and the spices over the packed onions. If the onions are above the level of the liquid use a spoon, bowl or anything to push the onions below the level of the hot vinegar. As the onions slightly cook they will soften up and stay below the surface.
Let the onions sit on the counter until cool. Server immediately or store in the fridge for up to a month.