Preheat oven to 350 degrees F (175 degrees C). Lightly grease an 8 inch pie plate.
Heat the olive oil in a skillet over medium heat. Add the red onions; cook and stir until tender and transparent, about 5 minutes. Stir in the garlic and pancetta, cook until the pancetta is crispy, about 8 minutes. Reduce heat to low. Mix in the spinach and feta cheese. Remove skillet from the heat.
Arrange the Provolone cheese to completely cover the bottom of the prepared pie plate. Spoon the spinach mixture over the cheese. Cover with the puff pastry sheet, trimming the edges to fit the pie plate. Brush top of pastry with the egg white.
Bake pie in preheated oven until the crust is golden brown, about 15 minutes. Cool 1 hour before serving.
