Combine the yogurt and lemon juice in a small bowl. Set aside.
Spoon ¼ cup of the granola into each glass. Top with about 1/3 cup of the lemon yogurt and ¼ cup of the raspberries. Spoon another ¼ cup of the granola on top of the berries and add another layer of lemon yogurt. Top each parfait with ½ cup blackberries and garnish with a lemon wedge and fresh mint, if desired.