Preheat oven to 400°F.
Toss rhubarb and strawberries with sugar, tapioca, salt, zest; in a large bowl, gently combine the rhubarb and the strawberries with the sugar, tapioca, salt, and orange zest. Let sit for 10 minutes.
Roll out 1 pastry dough disk, line pie dish, fill with strawberry rhubarb filling: Roll out your pastry dough and line the bottom of a pie dish with it. Trim to ½ inch from the edge. Place the filling into a pastry lined pie dish.
Roll out second dough disk, place on top of filling, trim, crimp, score: 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 the top and bottom edges together. Cut slits in the top for the steam to escape.
Bake: 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. The pie is done when the crust is nicely browned and the filling is thick and bubbly. Remove from oven and let cool on a rack.
Serve warm or cold. If you do cool it to room temperature, the juices will have more time to thicken.