Preheat oven to 400°F.
Begin making the dough for the crust. In a food processor pulse together the all purpose flour and cubed butter until you get coarse sand with clumps of butter.
Add the water. Add the cold water to the butter-flour mixture and pulse again until the mixture is moistened and stays together when squeezed in your hand.
Form the dough into a disc. Turn it out onto a lightly floured surface and gently form into a flat disk.
Wrap and cool the dough. Wrap the dough in plastic wrap and put it in the fridge for at least an hour.
Make the filling. In a large bowl mix together the ricotta, lemon zest, aleppo pepper, herbs, and salt.
Roll out the dough. Unwrap the dough and place it on a lightly floured surface. Roll it out into a large circle (it doesn’t have to be perfectly shaped). You want it at least 12 inches in diameter, pretty thin. Transfer it to a parchment paper lined baking sheet.
Assemble. Leaving a 2-inch border of crust, spread out the caramelized onion jam on the dough. On top of that spread out the creamy ricotta filling. Lastly place the thin rounds of zucchini slices over top, overlapping where needed.
Fold up the sides. Once all the filling is in, fold the dough edges up over the filling. Brush the crust with olive oil and drizzle some over the zucchini as well. Sprinkle the whole thing with a pinch of salt.
Bake. Put the galette into a preheated 400°F oven and bake for 40 minutes until golden brown.