Mix together sugar, salt, lemon juice and lemon zest. ( 1 or 2 Tbsp of bourbon or Grand Marnier are a delicious option here, if you like)
Leave the fruit to macerate in the sugar for about an hour.
Drain the liquid and reserve.
Stir the vanilla into the fruit.
Roll out the cold dough on a lightly floured surface. Roll into a large, round-ish circle about ¼ inch thick. Do not worry if it's not perfect.
Preheat the oven to 350°
Line a baking sheet with parchment paper.
Place dough on the baking sheet and sprinkle bottom of with rolled oats. (The rolled oats will absorb the fruit juice so you will not have a soggy crust.)
Spoon the fruit into the middle of the dough leaving a 2-inch border. Fold the edges into the center and over the fruit.
Brush folded dough with the egg wash. Dust with about a tablespoon of sugar and bake for approximately 45 minutes, or until the center is bubbly and the edges of the crust are golden brown.
While the galette is baking, take the reserved juices and heat in a saucepan until very thick.
Remove the baked galette from the oven and drizzle with the reserved syrup.
Serve warm, or room temperature.
Galettes are completely adaptable. Simply swap out the strawberries and rhubarb for any fruit that is in season.