For the dough:
Mix well the flour, sugar, the margarine cut into cubes and the lemon zest in a food processor. Then, place this mixture and the egg in a large bowl. Knead with your hands until obtain a compact mixture.
Place the pastry over a table and mold it in a square shape. Wrap the pastry in cling film and refrigerate for approximately 45 minutes.
Preheat the oven to 180ºC / (350ºF). Remove the pastry from the fridge, place it on a table with parchment paper and roll out the pastry with a rolling pin dusted with some flour. Line a pie pan (24 centimeters / (9 1/2 inches)) with the pastry, prick the bottom with a fork and place some dried beans for the dough doesn’t rise when it goes to the oven. Bake about 25 minutes until slightly golden.
Turn off the oven, remove the parchment paper and the beans and let the dough cool to room temperature.
For the filling:
In a electric mixer, whip the cream with one tablespoon powdered sugar until stiff peaks form. Reserve in the fridge.
Put the gelatin sheets in water about four minutes. Drain them well and put them in a bowl. Melt for 1 minute in the microwave. Remove from microwave and stir with a fork; set aside.
In a bowl, whisk the mango pulp and the yoghurt. Add the melted gelatin sheets and mix well. Finally, add the whipped cream and fold gently with a spatula.
Pour the mixture inside the dough and refrigerate until set (about 4 hours).
In a bowl, put the chocolate broken into pieces and the margarine. Melt for 1 minute in the microwave. Remove from microwave, pour the cream and stir well with a fork until obtain a creamy mixture.
Remove the pie from fridge, garnish with chocolate and serve.