In a large bowl mix brown millet flour, white rice flours, potato starch, baking powder, and salt
Add milk, yogurt and margarine and - using a fork or a spoon - mix and incorporate as much dry ingredients as possible, until you have a crumbly mixture
Work the mixture with your hands, pressing all the ingredients together
Move the dough to a worktop and keep working the dough untill you get a smooth ball of dough
Place in a bowl and refrigerate for 15-20 minutes
In the meantime slice the heirloom tomatoes ⅓ inch thick and the cherry tomatoes in half
Pre-heat the oven at 180°C/360F
Remove the pastry dough from the fridge and roll it out over a piece of parchment paper (flour the top with rice flour, place another piece of parchment paper on top and roll the dough out)
Spread a layer of fresh basil pesto on the rolled out crust, leaving out a couple inches along the edges Cover the pesto layer with a couple layers of sliced tomatoes, sprinkle with salt, dried oregano and drizzle with olive oil
Fold the edges over the filling and brush them with olive oil or plant based milk
Bake in pre-heated oven for 40 minutes, until the crust is golden and tomatoes are lightly roasted
Serve still warm or enjoy at room temperature!