Watermelon Ceviche

In a molcajete or grinder, crush/grind the garlic, oregano, and chiltepin powder and add the juice of one lime to make the process easier and the salt so this one dissolves, and then add it to a bowl if you are not using a molcajete or if it is too small. Add the juice from the rest of the limes and the diced watermelon and mix to ensure the juice gets in all the fruit; add the rest of the chopped/diced vegetables and let it sit in the fridge for at least 30 minutes before you serve. I recommend you eat it over tostadas with spread mayonnaise.