Preheat oven to 350°F. Line a large baking sheet with silicone liner or parchment paper.
Unroll the pie dough onto a well-floured surface. Using a 5 inch cookie cutter or a 5 inch bowl, cut out as many circles as possible. Using a rolling-pin, roll out the scraps and continue to cut out more circles until the dough runs out. We got 6 (5-inch) circles.
Mix the blueberries, blackberries and the raspberries with sugar, lemon zest and chopped thyme leaves.
Place about a tablespoon and a half of berry mixture in the center of the cut out dough circle, leaving an inch of border.
Gently fold the over the edges of the crust, folding the dough in on itself to create a pleated rim. Repeat with the rest of the dough circles. Place them in the prepared baking sheet.
Make an egg wash by beating together the egg and water. Brush edges of each mini galette with the egg wash and sprinkle the crust with turbinado sugar.
Bake for 20 minutes or till the berry filling is bubbly and the crust is golden.
Let the mini galette cool in the baking sheet for 5 minutes and then let it finish off cooling on a wire rack.
Serve at room temperature or slightly warm with a dollop of whipped topping and/or more fresh berries. (Optional)