Heat oven to 350°F degrees. Make the filling: Wilt spinach in a dry pan. Drain off excess moisture and chop finely. In a small bowl, fold into pesto. Mixture should be tapenade-thick. Add feta and lemon zest. Stir to combine. Adjust seasonings to taste and set aside. Assembly: Roll sheets of puff pastry out flat on large pieces of parchment paper (dusting with flour if pastry sticks). Using a large plate or lid as a guide, trace a 10 or 12-inch circle into the dough and make clean cuts, discarding excess dough. Chill one dough circle in the fridge until needed. With first dough round, spread filling out from the center, leaving a ½ -inch space from the outer edge. Dab edges with egg wash and place second dough round on top. Using a small drinking glass as a guide (roughly 2 inches in diameter), hold it in the center and divide the tarte into quarters -- cutting out and away from the center of the glass perimeter like spokes in a wheel. Divide each quadrant into 3-4 equal strips (so that you have 12-16 total spokes). If dough begins to get too pliable at any point, simply freeze for a few minutes and continue. Remove glass and place a finger near the center of each strip (where it is most likely to break), and gently twist each strand 3-4 times, gently pinching off each outer edge to secure. Freeze for 10-15 minutes. Brush top of pastry with egg wash. Bake for 30 to 35 minutes, until golden brown all over. Remove tart from oven and cool briefly before transferring to a platter for serving. Garnish with finely grated Parmesan.