Thaw the pineapple chunks and chop the cucumber into pieces roughly the same size as the pineapple chunks. Roughly chop the cilantro.
Prepare the dressing by whisking together the gochujang, rice vinegar, and sugar until dissolved.
Combine the cucumber, pineapple, cilantro, and dressing in a bowl. Serve immediately, or refrigerate until ready to eat. Stir the salad just before eating to redistribute the dressing.