Preheat oven to 400 degrees and prepare 6 muffin cups with paper liners or grease.
Stir together 1 1/2 cup flour, 3/4 cup sugar, salt, baking powder and 1 teaspoon cinnamon.
Mix in oil, egg and milk and stir until well combined. Fold in chopped apples.
Spoon muffin batter into the cups, filling to the top of the cup.
In a small bowl, stir together 1/2 cup sugar, 1/3 cup flour, butter and 1 1/2 teaspoon cinnamon. Mix together with a fork until well combined. Sprinkle mixture over the top of the unbaked mixture.
Bake for 20-25 minutes until a toothpick inserted into the center of a muffin comes out clean.