Preheat oven to 375°F. Remove dough from fridge. Allow to sit at room temperature for 5-7 minutes. Working on a lightly floured surface, roll one dough into a 9x8-inch rectangle. Cut in half to form two 9x4-inch rectangles. Cut each into thirds crosswise to form three 4x3-inch rectangles. You will end up with 6 rectangles. Repeat with second dough.
Place 6 rectangles on a parchment lined baking sheet. Add one tablespoon of chia strawberry jam in the center of six rectangles, leaving a small border along the edges. Moisten edges with milk or water. Top with remaining rectangles. Press edges with floured fork to seal.
Dock assembled pastry with a fork to allow for air to escape during baking. Brush tops with milk.
Bake for 17-20 minutes until tarts are golden brown. Let cool in pan for 2-5 minutes and then transfer to wire rack. Prepare glaze.