In a medium bowl, mix the Greek yogurt with the vanilla extract and honey or maple syrup if using. Stir until well combined.
In serving glasses or bowls, layer 1/4 cup of the yogurt mixture at the bottom.
Add a layer of mixed berries (about 1/4 cup) on top of the yogurt.
Sprinkle a layer of granola (about 2 tablespoons) over the berries.
Repeat the layers until the glasses are filled, finishing with a layer of berries on top.
If desired, sprinkle chia seeds over the top layer of berries for added nutrition.
Garnish with fresh mint leaves if desired. Serve immediately or chill in the refrigerator for up to 30 minutes before serving.