Preheat your oven to 425°F (220°C).
In a mixing bowl, combine the sliced strawberries, chopped rhubarb, granulated sugar, flour, salt, vanilla extract, and lemon juice. Toss until the fruits are evenly coated. Set aside to let the mixture rest for about 10 minutes.
Roll out one of the pie crusts and fit it into the bottom of your pie dish. Trim excess crust hanging over the edges.
Pour the strawberry-rhubarb filling into the pie crust, making sure to distribute it evenly.
Dot the filling with small pieces of butter.
Roll out the second pie crust and place it on top of the filling. Trim and crimp the edges to seal the pie. Cut several small slits in the top crust to allow steam to escape.
Place the pie on a baking sheet to catch any drips and bake in the preheated oven for 45 minutes, or until the crust is golden and the filling is bubbling.
If the edges of the crust begin to brown too quickly, cover them with aluminum foil.
Remove the pie from the oven and let it cool at room temperature for at least 2 hours before slicing.