In a small saucepan, combine the 2 cups of milk with the can of coconut milk and ½ cup of sugar, and bring to a simmer over medium-low heat.
Stir in the tapioca, turn the heat down to low, cover the pot, and cook - stirring occasionally - for about 30 minutes. When the tapioca is done cooking, the little pearls will turn clear.
Remove the tapioca from the heat and stir in the vanilla extract, salt, about half of the pineapple tidbits, and juice from one lime.
Stir the diced mango, half of the pineapple tidbits and ½ teaspoon of the lime zest together in a small bowl
Spoon a dollop of tapioca pudding into a cup, then layer in a spoonful of the fruit mixture, then layer in another spoonful of the tapioca pudding. Finally, top the pudding the more of the fruit mixture and a little extra lime zest