Melt the butter in a skillet large enough to hold the leeks, zucchini and peas.
Add the leeks and a couple tablespoons of water and cook over low heat until soft. Add the peas.
Add the mint, herbs and lemon zest to the peas and leeks. Stir in the squeezed zucchini and cook for 4 to 5 minutes. Season to taste with salt and pepper.
Chop, roughly shred or break the mozzarella into large pieces and scatter over the vegetables. Remove from heat and set aside.
Preheat the oven to 350°F/180°C and prepare a baking sheet with parchment paper.
Roll the dough into a 10 inch circle or oval. Transfer to the baking tray and pile the filling into the center of the dough. Fold the sides up and over the filling, leaving the center open. Brush the dough with egg wash.
Bake for 35 - 40 minutes or until the crust is cooked through and a good color. Let stand for 10 minutes before serving.