Preheat the oven to 325°F. Grease a 9x5-inch loaf pan and line it with parchment.
Whisk the almond flour, coconut flour, baking powder, and salt in a bowl until no clumps remain.
In a large bowl, whisk the eggs and powdered allulose until pale and slightly thickened. Whisk in the Greek yogurt, melted butter, orange zest, orange juice, vanilla extract, and orange blossom water.
Fold the dry ingredients into the wet ingredients until a smooth, scoopable batter forms. Rest the batter for 5 minutes.
Spread the batter into the loaf pan and level the top. Bake for 42 to 50 minutes, until the loaf is golden and a toothpick comes out clean.
Cool in the pan for 20 minutes, then transfer to a rack to cool completely.
Stir the powdered allulose, heavy cream, and orange blossom water into a light glaze. Drizzle over the cake and sprinkle with chopped pistachios.