Preheat oven to 330 F. Line a rectangular sheet tray with parchment and lightly spray with coconut (or other) cooking oil. Set aside.
Prepare your flavoring of pistachio, cranberry and lemon zest. I recommend using a kitchen scale for this. Set aside.
Combine your flour, caster sugar and baking powder in the bowl of a stand mixer fitted with a paddle attachment. Mix on low to combine.
Next, whisk 3 eggs in a large mixing cup or other bowl. You will likely not need to use all 3 eggs; I usually use about 2.5. Add the eggs slowly, a little at a time, mixing on low and continuing just until mixture begins to form a rough crumble and come together. Be careful that mixture is not wet or it will be harder to handle.
Add in your cranberries, pistachios and zest, mixing on low or using your hands to combine and bring the dough together.
Generously flour a cutting board with more gluten free flour and turn out your dough, kneading it by hand a few times to bring it together. Divide into two equal portions and form into two logs about 10 inches long.
Transfer each log to the prepared baking sheet and bake on middle oven rack for 30-35 minutes or until just starting to turn lightly brown.
Remove from oven and let sit at room temperature for 15 minutes or until cooled.
Place biscotti logs on cutting board. Using a serrated or sharp knife, slice logs into approximately one-inch pieces.
Place a fresh piece of parchment on your baking tray and arrange biscotti cut side down (sideways) on tray. Bake for another 12 minutes. Flip biscotti bake on opposite cut side for an additional 12-15 minutes or until dried and crunchy.
Let cool and serve or store in airtight container for up to a month.