Preheat the oven to 350 degrees. Spray a 9x13 baking dish with cooking spray and set aside.

Wash and dry the strawberries and rhubarb. Slice the strawberries and dice the rhubarb to bite-size pieces. Add them to the baking dish.

Using a lemon zester, zest the lemon over the freshly cut fruit. Cut the lemon in half and squeeze the juice over the strawberry-rhubarb mix (be sure the strain for lemon seeds).

In a medium-size mixing bowl, combine the gluten-free flour blend and cane sugar. Stir together. Add the dairy-free butter, starting with 4 tablespoons. Cut into the flour-sugar mix. If more butter is needed to create a thick crumble, add one tablespoon of butter at a time until a thick crumble has formed.

Evenly sprinkle the crumble over the fruit mixture. Place the baking dish in the oven and bake for 40-45 minutes or until the fruit is bubbling and the crumble is light golden brown. Remove from the oven, let cool, and then serve.