Preheat oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners.
In a large bowl, whisk together flour, sugar, salt, and baking powder.
In a separate bowl, combine oil, egg, milk, and vanilla extract.
Mix wet ingredients into the dry until just combined (do not overmix).
Gently fold in the blueberries.
Divide the batter evenly into muffin cups (about ¾ full).
(Optional) For streusel topping: combine sugar, flour, butter, and cinnamon until crumbly. Sprinkle over muffin batter.
Bake for 20–25 minutes, or until golden brown and a toothpick inserted comes out clean.
Let muffins cool slightly before serving.