Prepare your pie crust and set aside. Pre-heat oven to 400 degrees F (204 C). Put the tapioca pearls into a blender and blend until they are very small.

Wash the strawberries and use a paring knife to remove the green leaves and the white bit inside the stem. (This is called "hulling" strawberries.") Slice into 1/4" thick slices (0.6 cm) and set aside.

Wash the rhubarb, dry, and slice into 1/2" thick slices (1.2 cm). Make sure you do not include any leaves, as they are toxic.

Drain the cherries, reserving the juice for another use. Mix all the fruit in a bowl with the zest from one lemon, agave syrup, salt, and the ground tapioca. Toss well to mix.

Put the pie crust into your pie dish. Pour in the filling. Put on the top crust and crimp well around the edges so it's completely sealed. Cut slits in the center to allow steam to escape.

Bake for 20 minutes, then turn down the oven to 350 F (175 C) and bake for 20 minutes more. Check for doneness and to make sure the filling isn't boiling over. You can put a cookie sheet on the rack below to catch drips. Bake until the crust is golden and flaky and the filling is bubbling.

Cool on a rack at least 15 minutes before slicing.