- With the rack in the middle position, preheat the oven to 350°F (180°C). Line a baking sheet with a silicone mat or parchment paper.
- In a bowl, combine the flour, sugar, baking powder and pistachios. Add the oat beverage, oil and lemon zest.
- With lightly floured hands, spread the mixture onto the baking sheet and form into a 12 x 4-inch (30 x 10 cm) rectangle.
- Bake for 30 minutes or until a toothpick inserted in the centre of the dough comes out clean. Let cool for 5 minutes, then transfer to a work surface and let cool for 10 minutes more.
- Using a bread knife, cut the rectangle into slices ½ inch (1 cm) thick. Spread out on the baking sheet (use a second baking sheet as needed).
- Bake one sheet at a time for 16 minutes, turning the biscotti over halfway through, or until golden. Let cool completely.