In a medium bowl, whisk flour, baking powder, and salt. In a large bowl, using an electric mixer on medium-high speed, beat granulated sugar and butter until combined and fluffy. Add eggs one at a time, beating to blend after each addition. Stir in vanilla and orange zest until combined. Add dry ingredients and stir until just combined and no visible streaks remain. Fold in cranberries.
Turn out dough onto a large parchment-lined sheet pan and divide into 2 pieces (about 500 grams each). Lightly wet your hands and shape each piece into a rectangular slab about 9" long, 4" wide, and 3/4" thick. Arrange dough so longer edge of rectangle is parallel to shortest edge of sheet tray so it has room to spread. Chill dough until cold, about 30 minutes.
Preheat oven to 350°. Bake biscotti until edges start to turn golden brown and center doesn’t feel sticky or soft to the touch, about 35 minutes. Let cool 10 minutes.
Slice each loaf into 10 slices. Carefully arrange slices cut side down on sheet pan. Continue to bake, flipping halfway through, until both sides are dry and light brown, about 15 minutes more. Transfer to a wire rack and let cool completely.
Meanwhile, in a medium heatproof bowl, microwave chocolate and oil in 30-second increments, stirring between each, until chocolate is melted and smooth. Place pistachios in a deep bowl or on a plate. Dip one end of biscotti into chocolate, then into pistachios, turning to coat.