In a medium glass bowl, whisk together chia seeds, milk, vanilla extract, sweetener and a pinch of salt.
Let sit 10 minutes, then whisk again. Cover and place in the refrigerator for 4 hours or overnight. Place mango, milk or water and sweetener in a blender and puree until smooth.
Scoop chia seed pudding into dessert glasses, then top with mango puree. Garnish with berries and mint.