To make the crust: Whisk together the dry ingredients. Work in the butter until the mixture is crumbly. Drizzle in 5 tablespoons of water, stirring gently until everything is evenly moistened; add the final tablespoon of water if necessary to make a cohesive dough., Pat the dough into a disk, wrap, and refrigerate for 30 minutes., To make the filling: Preheat the oven to 425°F. Lightly grease (or line with parchment) two baking sheets., Place the zucchini slices on one pan and sprinkle with 1 1/2 teaspoons pizza seasoning., Place the tomato halves on the second pan and sprinkle with the remaining pizza seasoning., Roast the zucchini and tomatoes until tender, about 15 to 20 minutes for the zucchini and 10 to 15 minutes for the tomatoes., Remove the zucchini and tomatoes from the oven and allow to cool for 10 minutes., Combine the ricotta, salt, pepper, lemon zest, and egg until evenly blended. Set aside., To assemble the galette: On a lightly floured work surface, roll the dough into a 12" circle. Transfer the dough to a parchment-lined baking sheet., Spread the ricotta mixture over the dough, leaving a 2"-wide bare strip along the perimeter., Sprinkle half the Parmesan over the ricotta, then shingle the zucchini slices over the cheese and scatter the tomato halves on top., Fold the bare edges of the dough into the center., Brush the exposed edges of the crust with egg wash, and sprinkle the remaining Parmesan over the whole galette., Bake the galette for 25 to 30 minutes, until the crust is golden brown and the filling is bubbling., Remove the galette from the oven and allow it to cool for 5 to 10 minutes before serving.