Place oven rack in bottom third of oven and preheat to 400°F.
Roll out 1 half of the pie crust dough to a rough 13-inch circle. Transfer to a 9-inch pie dish.
Roll out second pie crust and have it ready and waiting. You can leave it whole or cut into strips to form a lattice.
In a large bowl, combine the cornstarch, sugar, orange zest and salt. Add the strawberries and rhubarb and toss to coat. Dump mixture into the prepared pie shell.
Carefully transfer top crust over the top of the pie filling. Pinch the top and bottom crusts together and tuck into the pie dish. Pinch the edges decoratively, if desired. If you left the top crust whole, cut steam vents into the center with a sharp knife. Brush with egg wash.
Place the pie on a sheet pan and bake in the oven until crust is golden and filling in the center is bubbly, 60-75 minutes. If the crust browns too quickly, cover with foil to prevent it from burning.
Remove from oven and let cool to room temperature for at least 2 hours before slicing and serving.