Prepare the pineapple: Cut fresh pineapple into 1-inch thick spears or bite-sized chunks, removing core and skin. Pat pieces completely dry with a clean kitchen towel or paper towels.

Set up for freezing: Line a baking sheet with parchment paper. Arrange pineapple pieces in a single layer on the prepared sheet.

Flash freeze: Place the baking sheet in the freezer for 15 minutes. This helps the chocolate set quickly and prevents it from sliding off.

Melt the chocolate: While pineapple is freezing, place chopped chocolate in a microwave-safe bowl. Microwave at 50% power in 30-second intervals, stirring between each interval, until smooth and melted (about 2-3 minutes total). Let cool slightly.

Dip the pineapple: Remove pineapple from freezer and quickly pat dry again if any condensation formed. Using a fork or toothpick, dip each piece halfway into the melted chocolate, allowing excess to drip off. Return to the parchment-lined baking sheet.

Add toppings: Immediately sprinkle each chocolate-dipped piece with flaky sea salt or tajin while the chocolate is still wet.

Set and serve: Let chocolate set at room temperature for 10-15 minutes, or refrigerate for 5 minutes for faster setting. Serve immediately for best texture.