Preheat your oven to 350°F (175°C) and get your 9x13x2-inch baking dish ready by greasing it.
Using an electric mixer, beat in the grated carrots, drained mandarin oranges, oil, eggs, vanilla extract, and orange zest. Beat until the batter is smooth, about 2 minutes.
Pour the batter into the prepared baking dish and bake in the preheated oven for 40 to 50 minutes or until a toothpick inserted into the center comes out clean.