In 2- to 3-quart trifle bowl or clear glass bowl, arrange half of the cake cubes. Top with 2 cups of the blackberries. Top with blackberry yogurt mixture. Arrange remaining cake cubes over yogurt. Top with remaining blackberries. Spoon lemon yogurt mixture over berries. Sprinkle with lemon peel. Refrigerate until ready to serve. Cover and refrigerate any remaining trifle.