In a medium bowl, mix the chia seeds and almond milk together and stir with a fork. Let it sit for 10 minutes and stir, breaking apart any large chunks. Let it sit again for another 5 to 10 minutes and stir.
Add the agave and vanilla extract and mix until well incorporated. Cover the bowl with plastic wrap and refrigerate for at least 4 hours. If you are planning to refrigerate this overnight, put the chia pudding in an airtight container and refrigerate.
When you are ready to eat the chia pudding, thaw the mangoes by immersing them in very warm water (the water should not be burning hot). Ten minutes was long enough to thaw the mangoes for me. Puree the mangoes in a food processor or blender.
Mix the pureed mango and chia pudding together.
Serve chilled and top the pudding with your favorite toppings!