For the crust: Mix the flour, sugar and salt. Drizzle the olive oil over the flour and cut in with a fork, combining lightly until the mixture resembles coarse meal. Sprinkle water over the flour, a tablespoon at a time, and mix lightly with a fork. (These two steps can also be done in a food processor, if you use a light touch with the "pulse" button.) With your hands, press the pastry lightly into a ball, wrap in waxed paper, and let rest in the fridge at least 20 minutes.
While the dough is resting, make the filling: Mix together the cinnamon, ginger, flour, sugar and salt. In a large bowl, toss the apple and pear slices with the dry mixture. Drizzle lemon juice over the top.
Prepare the galette: Preheat the oven to 375 degrees and line a baking sheet with parchment paper.
On a wide surface, roll out the dough between two sheets of parchment paper until it becomes a 1/4-inch-thick circle. Arrange the fruit mixture in the middle of the dough, and loosely gather the dough around the fruit, leaving an opening at the top (the dough won't close completely). Place the galette on the parchment paper and bake in the middle of the oven until filling is bubbly and crust is lightly browned, about 35 to 40 minutes.