In a blender, combine the cubed pineapple and blend until smooth. You can strain it if you prefer a smoother texture, but keeping the pulp adds a nice texture.
In a large pitcher, add the fresh mint leaves and lime juice. Use a muddler or the back of a spoon to gently crush the mint leaves to release their essential oils, being careful not to shred them too much.
Pour the pineapple puree into the pitcher with the mint and lime mixture. Mix well.
Add the agave syrup (or honey) and stir until well combined. Adjust the sweetness to your liking.
Fill glasses with ice cubes and pour the pineapple-mint mixture over the ice.
Top off each glass with sparkling water and stir gently to combine.
Garnish with pineapple slices and mint sprigs before serving.
Notes
Adjust the sweetness according to your preference.