In a bowl, combine pineapple, onions, cilantro, lime juice, 1 to 2 Tablespoons of chopped jalapeno (or to taste), and a pinch of salt.* Fully combine all of the ingredients. Taste & adjust with more lime juice, salt, or jalapeno. (Keep in mind that the heat will intensify a little as the salsa sits.)
You can serve the salsa & eat it right away. However, it tastes best after the flavors have had time to mingle and marry. Cover the salsa & refrigerate for 4 or more hours for the best flavors. Serve with tacos, nachos, or tortilla chips for dipping.
*You can simply combine all of the ingredients in a bowl. Or for even sizes & mixing, put the ingredients into a food processor instead. Pulse a few times to get everything mixed, stopping once or twice to scrape down the sides for even chopping.