In a large mixing bowl, combine the sliced strawberries and chopped rhubarb.

In a separate small bowl, whisk together the granulated sugar, cornstarch, ground cinnamon, and salt until evenly mixed.

Sprinkle the dry mixture over the strawberries and rhubarb, then gently toss to coat the fruit evenly.

Add the lemon juice to the fruit mixture and stir gently until the sugar and cornstarch begin to dissolve and coat the fruit evenly.

Let the mixture sit for about 10 minutes to allow the fruit to release its juices and the flavors to meld together.

Transfer the pie filling to an unbaked pie crust or store it in an airtight container in the refrigerator until ready to use.