Preheat oven to 450F. Make the pre-baked pie crust. In a bowl combine the rhubarb, strawberries, cornstarch, water or juice, and sugar. Mix well to coat the fruit with cornstarch and sugar, then let sit for 10 minutes. Fill the pre-baked pie shell with the fruit mixture. Cover the edges of the crust with foil to prevent browning. Bake for 10 mintues at 450F, then reduce heat to 350F, and continue baking for 25 to 30 minutes. Remove the pie from the oven, and let it cool to room temperature before serving.