In a medium bowl, whisk the chia seeds, almond milk, Greek yogurt, maple syrup and vanilla until evenly combined and no dry clumps remain.
Let the mixture sit 5 minutes, then whisk again to break up any clumps that formed.
Divide between two 8-ounce jars or glasses. Cover and refrigerate at least 4 hours or overnight, until thick and spoonable.
Stir well before eating. If the pudding is thicker than you like, stir in 1 to 2 tbsp more almond milk.
Top with the berries and sliced almonds and serve cold. Store covered in the fridge up to 3 days.