Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch cake pan.
Beat oil and eggs in a large bowl with an electric mixer until creamy. Add sugar and vanilla extract; beat until well combined.
Sift flour, cinnamon, baking soda, and salt together in a medium bowl.
Gradually stir flour mixture into oil-egg mixture until just combined; batter will be very thick. Fold in apples using a wooden spoon or spatula.
Spread batter into the prepared pan.
Bake in the preheated oven until a toothpick inserted in center comes out clean, about 45 minutes. Cool cake on a wire rack before slicing.
