Soak the dates in hot water for 10 minutes, then throw excess water and deseed the dates. Peel the mangoes and roughly chop into chunks. Squeeze any pulp left on the seed. Add the dates, mango and lime juice into a blender and puree till its a thick, uniform pulp. This pulp should be thick, do not add any water. Taste for sweetness, if mango is not sweet enough, soak more dates and blend again. Place in a bowl, add the chia seeds, stir through and set aside for 30 minutes.