Preheat oven to 400°F.

Roll out your pastry dough and line the bottom of a pie dish with it. Trim to 1/2 inch from the edge. Put dish in refrigerator to chill.

In a large bowl, gently combine the rhubarb and the strawberries with the sugar, tapioca, salt, and orange zest. Let sit for 10 minutes.

Place the filling into chilled pastry lined pie dish. Roll out the second pastry dough and place over the pie. Trim the edges to an inch from the edge of the pie dish. Tuck the top crust edges over the bottom crust edges and use your fingers or a fork to crimp to seal edges together. (I like to add a glaze and sprinkling of course sugar on my pies, by using a pastry brush to brush a thin layer of egg white over the top of the pie and sprinkle with sugar.) Cut slits in the top for the steam to escape.

Place pie on the middle rack of a 400°F oven, with a baking sheet on a lower rack to catch any juices that might spill over. Bake for 20 minutes at 400°F, then reduce heat to 350°F, and bake an additional 40-50 minutes longer (50 to 60 minutes longer if doing a 10-inch pie). The pie is done when the crust is nicely browned and the filling (that you can see through the venting holes) thick and bubbly. Remove from oven and let cool on a rack.

Serve warm or cold. If you do cool to room temperature, the juices will have more time to thicken.