Bring the sugar and 50 ml (approximately 2 ounces) of water to a boil. Reduce the heat and let simmer for 5 minutes. Remove from the heat, cool slightly, then stir in the lemon liqueur.
Heat the grill. Halve the cantaloupe and scrape out the seeds. Brush the cut surfaces generously with the syrup. Place the cantaloupe on the grill. Cook for 10 minutes, turning occasionally. Rinse the raspberries and pat dry.
Remove the cantaloupe from the grill, and arrange on plates. Garnish with freshly ground black pepper and serve with the raspberries.