Drain pineapple in a colander set over a bowl, reserving juice for another use. You should have about 1 3/4 cups fruit and 1 cup juice. If you like, roughly chop about half of the pineapple to have a mixed texture.
Transfer the pineapple to a bowl. Add the diced jalapeño, onion, and cilantro. Mix well, then add salt and pepper to taste, keeping in mind how you plan to serve it. Use less salt if serving with salty chips, or more if serving on grilled meat.
Serve immediately, or cover and chill until ready to eat. The salsa will get juicier as it sits; simply stir it back up to incorporate.
Notes
Makes about 2 cups.
For a hotter salsa, leave the seeds in the jalapeños or swap with serrano peppers.
Nutrition information is an estimate based on online calculators and provided as a courtesy. Any nutritional information should be used as a general guideline only.