1. Prepare the pineapple by peeling, coring, and cutting into small pieces; set aside. If using jalapeños, thinly slice and remove seeds for milder heat if desired.
2. In a medium to large saucepan, combine sugar, apple cider vinegar, lemon juice (if using), and spices such as red pepper flakes, mustard seeds, turmeric, ginger, and garlic if included. Bring to a gentle boil over medium heat, stirring until sugar dissolves.
3. Add pineapple chunks and jalapeños to the syrup. Reduce heat to low and simmer for 10 to 20 minutes, stirring occasionally. Simmering time depends on desired texture—shorter for chunkier candy, longer for softer, syrupy relish.
4. Remove from heat and let cool slightly. Stir in fresh mint leaves if desired.
5. Transfer the mixture with syrup into sterilized jars. For longer shelf life, process sealed jars in a hot water bath for 10 minutes, or refrigerate for short-term storage.
6. Store in refrigerator for at least 24 hours to allow flavors to meld; it improves with time and can be kept refrigerated for up to 2 weeks. For longer storage without canning, freeze in airtight containers for up to 3 months.