Preheat oven to 425°F.
PREPARE CRUST: Roll out pastry dough to a 9-10 inch circle on a lightly floured surface. You can use a homemade pie crust dough or purchased one. There is no need to trim the edges. A "rustic" look is perfect! Fold dough in half, and carefully transfer dough to the middle of a 13x9 inch baking sheet. Unfold dough. Set aside.
PREPARE PEACH FILLING: In a large mixing bowl, mix together peeled, thinly sliced peaches (thawed and drained, if using frozen), granulated sugar, flour, cinnamon and lemon juice. Stir gently, to combine.
MAKE STREUSEL TOPPING: In a small mixing bowl, combine flour, brown sugar, cinnamon, and cold butter. Cut in butter using a pastry blender or two forks. Cut the butter in until the mixture is crumbly and the butter has been reduced to the size of peas. Stir in chopped pecans (or walnuts). Set aside.
ASSEMBLE GALETTE: Place the peach pie filling into the center of crust, slightly mounding up in middle. Be sure to leave about a 2-3 inch rim of BARE crust all around edges. Evenly distribute all of the streusel topping over peach filling, mounding up in the middle, also. Gently pull the crust up and slightly over the edges of pie/streusel filling, to form a roughly shaped "crust" that holds the filling in.
BAKE GALETTE: Place galette into preheated oven; bake for approx. 30-35 minutes, or until streusel topping and crust are golden brown. Pie filling should be cooked through and bubbly. Remove pan from oven to wire rack. Let galette cool (on baking sheet) for 10-15 minutes, before slicing (or transferring to serving platter. Serve as is, or with a scoop of vanilla ice cream. Enjoy!
NOTE: May use frozen peach slices, packed without syrup. Thaw completely and drain, before preparing filling.
Streusel Topped Peach Galette https://www.thegratefulgirlcooks.com/streusel-topped-peach-galette/