Position rack in oven middle and preheat to 350°. Oil bottom and sides of a 9-inch round cake pan. Line bottom with parchment paper circle. Do not oil paper.
Sift flour, baking powder, baking soda, cinnamon, nutmeg, ginger, and salt into a medium bowl. Whisk lightly to aerate ingredients.
In a second medium bowl, whisk maple syrup, milk, oil, vinegar, and vanilla until thoroughly blended. Pour into dry ingredients and whisk until smooth. Stir in grated carrots, walnuts, chocolate chips, and orange zest, if using.
Pour batter into prepared pan and smooth top. Bake 25–35 minutes or until top is golden brown, sides have pulled away from pan, and tester inserted in center comes out clean. Cool on a rack for 5 minutes. Run a thin knife around inside edge, and invert cake onto rack. Carefully peel off parchment paper. Invert again, and allow cake to cool completely before slicing and serving.