Preheat oven to 375 degrees F (190 degrees C). Grease an 8x8-inch baking pan.

Blend orange in the blender until liquified; measure 1 cup orange juice.

Whisk orange juice, flour, sugar, vegetable oil, baking soda, and salt together in a bowl. Pour batter into the prepared pan.

Bake in the preheated oven until a toothpick inserted in the center of the cake comes out clean, about 30 minutes.