1Thinly slice the red onion. Do not cut it this way, cut it the other way.
2Put the sliced onions into a glass jar.
3In a small saucepan, mix 1.5 cups of water, 1.5 cups of red wine vinegar, 3 roughly chopped garlic cloves, 1 tsp of peppercorns, 1 bay leaf, 1/2 tsp of oregano, and 0.5 tsp of ground chili arbol (optional).
4Add 3 tbs of sugar and 1.5 tbs of salt to the mixture.
5Boil the mixture.
6Carefully pour the mixture into the jar with the onions.
7Make sure to get the garlic and bay leaf into the jar.
8Let it sit for at least a few hours, overnight is best.