Preheat your oven to 350 degrees Fahrenheit.
Prepare an 8-inch round cake pan by lightly oiling it or lining it with parchment paper.
In a large mixing bowl, combine corn flour, brown rice flour, gluten-free all-purpose flour, baking powder, and ground ginger to create your dry mixture.
In a separate small bowl, mix the lemon zest and ½ cup of the coconut sugar together.
Whisk in the lemon juice, eggs, coconut milk, and olive oil to create the wet mixture.
Pour the wet mixture into the bowl with the dry ingredients and stir gently until just combined.
Pour the batter into the prepared cake pan, sprinkle the chopped rhubarb and sliced strawberries on top, and press them lightly into the batter.
Sprinkle 1 tablespoon of coconut sugar over the top of the cake.
Bake in the preheated oven for about 50 to 60 minutes, checking for doneness with a toothpick.
Allow the cake to cool before turning it out onto a cutting board. Slice into wedges and enjoy.
