Remove the tough grassy fibres from the ends of the coconuts.
One at a time, hold a coconut over a large bowl and use a heavy steel or the back of a large knife to hit both sides of the coconut until it cracks open. Reserve the coconut water.
Using a paring knife, separate the coconut flesh from the shells and roughly chop into small pieces.
Transfer to a food processor with the coconut water and 400ml water.
Blitz for 5-10 minutes, or until the mixture is thick and pulpy without any large chunks. Pour into a fine sieve suspended over a large bowl, pressing to strain all the liquid. (You will need 400ml coconut milk for the rice.)
Put the pudding or wholegrain rice, coconut milk, vanilla seeds and the pod, both sugars, cinnamon, ground cardamom seeds and lime juice in a saucepan. Stir to combine and set over a medium-high heat.
Bring to the boil, then reduce the heat to low. Cover with a lid and simmer gently for 45-50 minutes, stirring often, or until the rice is tender, creamy and all the liquid has been absorbed. Leave to cool with the lid on.
Peel and halve the mango, then remove the stone and thinly slice the flesh.
Divide the coconut rice between bowls and arrange the mango on top. Garnish with lime zest and serve.