1. Preheat oven to 350 degrees F.
2. In a large bowl, combine flour, sugar, salt, and baking powder.
3. Place vegetable oil into a 1-cup measuring cup. Add the egg and enough milk (approximately 1/3 cup) to equal 1 cup total liquid.
4. Mix the wet ingredients with the flour mixture. Fold in fruit.
5. Fill muffin cups right to the top with the blueberry batter.
6. To make the streusel topping, mix together sugar, flour, butter, and cinnamon. Sprinkle over top of muffin batter.
7. Bake for 30 to 35 minutes in the preheated oven, or until done.