Mix together rhubarb, strawberries, granulated sugar, cornstarch, zest and juice, and 1/4 teaspoon salt.
Put into the refrigerator while you make the pie crust.
Preheat oven: 425° F
Place flour into a food-processor. Add butter one third at a time, pulsing 3 times for each addition. Butter and flour should be combined with visible butter pieces (about pea size).
Add 3 Tablespoons. of ice water at a time, pulse to combine until dough starts to form a ball.
Pour dough onto counter. Press dough by hand. If it is not holding together, then add 1-2 more Tablespoons of ice water until dough comes together without falling apart.
Press into a log and cut into 2 pieces. Form into disks and wrap well with plastic. Chill for two hours.
Sprinkle flour on the countertop, and roll dough out from the center. Add flour and turn dough ¼ around each time as you roll. Roll out dough at least two extra inches than the pie plate. (Use the pie plate to measure).
Transfer dough to pie plate by rolling up around rolling pin.
Fill the pie with the fruit filling.
Roll second piece of dough the same size. Fit it over the filled pie.
Crimp the edges by rolling them up and pressing down with your thumb. Cut three small slices in the center. Brush the surface with vegan wash.
Sprinkle the top crust with sugar, and put into the freezer for 15 minutes.
Bake pie on middle rack, with foil-lined baking sheet under pan.
Bake for 20 minutes at 425° F.
Turn the temperature down to 350° F for another hour.
Check on the pie during the baking process. If it is browning too quickly, place foil around edges of the pie.
When done baking, transfer pie to a wire rack, and let cool.