In a large bowl, combine the chickpea flour and stevia. Add the tahini and use your fingers to incorporate it into the dry ingredients, so it will resemble bread crumbs. Pour in the water and stir well, then knead with your hands to get a smooth dough. Press the dough into a lined pie tin (mine was 20cm wide), trim any excess dough. Blind bake the crust for 10 mins at 180C, then continue from filling instructions.