Add zucchini and pepper and cook for a further 10 minutes
When the vegetables are cooked adjust salt and pepper to taste
the vegetables should be quite dry
if not add 1/2-1 tbsp flour and stir well while cooking another minute
so the liquid is absorbed
Let cool 5 minutes
then add the mozzarella cubes to the ratatouille
Roll out puff pastry so to have a 40x25 cm I think its about 20x12 5 inches rectangle
put the rectangle on a cookie sheet lined with baking paper
pour ratatouille and mozzarella mixture in the center of the rectangle and roll up
sealing the edges very well
Brush with the beaten egg yolk
make a few cuts on the surface so the steam can get out and put in preheated oven 200C for 25-30 minutes or until pastry is golden and crisp you might want to put another lined cookie sheet on the lower rack as
depending on the freshness of the mozzarella you use
the strudel may produce some liquid and drip
Let the strudel cool a little before slicing and serving