Muddle the lime juice, agave nectar and mint sprig in a Collins glass.
Add the pineapple juice and stir to combine.
Add crushed ice and top with the rum and grilled pineapple chunks.
Garnish with mint leaves.
*Grilled pineapple chunks: Remove the skin and top from a ripe pineapple and cut into 1/3-inch slices. Grill until caramelized. Cut into chunks.