In a pan, heat oil and cook onions and leeks in it for about 7-8 minutes. Then, add garlic to it and cook for another 2 minutes.
Take this mixture out of the pan and put it into a bowl.
In the same pan, add the chicken along with some salt and pepper and cook for about 3-4 minutes until it turns golden brown.
After that, add the mushrooms and cook them for 5 minutes. Also, add the ham and cook it as well.
Then, take another saucepan and melt butter in it. Add flour to it and cook it for a minute.
Remove the pan from heat and while stirring, add milk to it. When it has mixed, add the stock and keep stirring.
Place it over the heat again and bring this mixture to a boil.
Boil it for 5 minutes and then add lemon juice, zest, and parsley to it and mix.
Now, mix this sauce with the chicken and the onion mixture and pour it into a pie dish.
Preheat the oven at 200℃.
Roll out the puff pastry and cover the pie dish with it. Trim the excess pastry around the edges.
Brush the top with egg and make holes for steam to escape.
Place the pie dish in the oven and bake it for about 25 minutes until the top looks golden brown.
Meanwhile, boil peas and broccoli in water for 3-4 minutes.
Take the pie out and serve it with broccoli and peas.