Preheat the oven to 350°F (175°C), and grease and flour a 10-inch Bundt or tube pan.
In a medium bowl, toss diced apples with 1 tablespoon sugar and 1 teaspoon cinnamon; set aside.
Sift together the flour, baking powder, and salt.
In a large bowl, beat together 2 cups white sugar, oil, orange juice, vanilla, and eggs with an electric mixer on high until smooth.
Stir in the sifted dry ingredients, then gently fold in chopped walnuts.
Pour a third of the batter into the prepared pan, sprinkle with half the apple mixture, and repeat the layers, ending with batter.
Bake for 55 to 60 minutes, or until a toothpick inserted in the center comes out clean.
Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely.
Finish with a light dusting of confectioners' sugar.