Heat the oil in a large saucepan over medium heat. When the oil is hot, add the garlic, onion and jalapeno, if using, and cook until the onion is slightly cooked, but still crispy, about 5 minutes. Add the water and vinegar and bring to a simmer (see Cook's Note). Remove from the heat and add the oregano, peppercorns, bay leaves and zucchini noodles. Season with salt. Place in a jar without a lid and let cool slightly. When done cooling, place on the lid and refrigerate.
For safety, before adding the water and vinegar to the hot oil, sprinkle just a few drops of the liquid into the oil. If the oil splatters, then it needs to cool before adding the full recipe amount. Continue to test the oil with mere sprinkles of vinegar and water until no splattering occurs. At this time, it will be safe to add the full amount of vinegar and water.