Prepare the pineapple by removing the skin and core, then dicing the flesh into uniform 1/2-inch cubes.
Slice the English cucumber into quarters lengthwise, then cut crosswise into 1/4-inch thick slices.
In a large mixing bowl, combine the diced pineapple, cucumber slices, and thinly sliced red onion.
In a small vessel, whisk together the lime juice, olive oil, and sea salt until fully emulsified.
Drizzle the lime dressing over the fruit and vegetable mixture, tossing gently to coat.
Add the chopped cilantro and chili flakes, then toss once more to distribute.
Serve immediately or refrigerate for 15-30 minutes to allow the flavors to meld.