In a mixing bowl, combine the Greek yogurt and vanilla extract (if using plain yogurt). Stir until well blended.
In serving glasses or bowls, layer 1/4 cup of the Greek yogurt mixture at the bottom.
Add a layer of mixed berries (about 1/4 cup) on top of the yogurt.
Sprinkle 2 tablespoons of granola over the berries.
Repeat the layers until the glasses are filled, finishing with a layer of berries and a sprinkle of granola on top.
Drizzle honey over the top if desired, and garnish with fresh mint leaves.
Serve immediately or refrigerate for up to 2 hours before serving.