Preheat your oven to 375°F (190°C). Grease a baking pan.
In a mixing bowl, combine flour, sugar, baking powder, and salt.
Add milk, vegetable oil, and vanilla extract. Mix until just combined.
Fold in the blueberries gently.
Pour the batter into the prepared baking pan.
For the streusel topping, combine brown sugar, flour, butter, and cinnamon in a bowl. Mix until crumbly.
Sprinkle the streusel topping over the batter.
Bake for 45 minutes or until a toothpick inserted into the center comes out clean.
Let it cool before serving. Enjoy!