Preheat your oven to 400°F.
Season the pork tenderloins with salt and pepper.
In a skillet, heat olive oil over medium heat and sear the pork until browned.
Remove from the skillet and let them cool.
In the same skillet, add mushrooms and garlic.
Cook until the mushrooms release their moisture and become golden.
Stir in the spinach until just wilted.
Set aside to cool.
Roll out the puff pastry slightly and lay out the prosciutto slices on top.
Spread the mushroom-spinach mixture evenly over the prosciutto.
Place the pork tenderloin on top.
Whisk the egg with water to create an egg wash.
Brush the edges of the puff pastry with the egg wash.
Wrap the dough over the pork tightly and seal the edges.
Place the wrapped pork, seam-side down, on a baking sheet.
Brush the entire pastry with the remaining egg wash.
Bake in the preheated oven for about 25-30 minutes or until the pastry is golden brown and the pork is cooked to your liking.
Let it rest for a few minutes before slicing.