Preheat oven to 350oF (180oC).
Blend mango until smooth in food processor or blender to make a puree.
To a bowl, add mango puree and water. Whisk until well combined.
To same bowl, add sugar. Mix until sugar dissolves completely.
To same bowl, add oil, mix well and set aside.
In another bowl, sieve flour, baking powder, baking soda and salt. Then, add mango chunks. Gently coat mango chunks with flour. Do not crush the mango.
To this flour mixture, add the reserved mango puree mixture. Fold mango puree gently into flour until dry flour is no longer visible. Do not over mix.
Spoon batter into cupcake liners until 2/3 full.
Top cupcakes with pistachios.
Bake in preheated oven to 350oF (180oC) for 20-22 minutes, or until inserted toothpick comes out clean.
Let cupcakes cool down for 10 minutes in pan. Then transfer to cooling rack to cool down completely.