In a large measuring cup, combine the lemonade concentrate and 2/3 cup water; strain into a medium saucepan. Sprinkle the gelatin over the liquid and let soften for 2 minutes. Heat over low heat, stirring constantly, until the gelatin is dissolved, about 5 minutes; stir in the vodka.
Pour the mixture into a 4-by-8-inch loaf pan and refrigerate until firm, about 4 hours. Cut into 24 pieces. Garnish each piece with the lemon zest.
