Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
In another bowl, mix the milk, vegetable oil, and eggs until well combined.
Add the wet ingredients to the dry ingredients and stir until just combined.
Divide the batter evenly among the muffin cups.
In a small bowl, combine the brown sugar, flour, and cinnamon for the streusel topping. Stir in the melted butter until crumbly.
Sprinkle the streusel topping evenly over the muffin batter.
Bake for 20 minutes or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.