Preheat the oven to 375°F (190°C) and grease the muffin tin.
Whisk together 2 cups of all-purpose flour, 1 cup of granulated sugar, 1 tablespoon of baking powder, and 1/2 teaspoon of salt in a large mixing bowl.
Mix 1 cup of milk, 1/2 cup of vegetable oil, and 1 large egg in another bowl until thoroughly combined.
Pour the wet ingredients into the dry mixture and stir gently until just combined, then fold in 1 cup of fresh blueberries.
Combine 1/2 cup of all-purpose flour, 1/3 cup of brown sugar, 1/4 cup of softened unsalted butter, and 1/2 teaspoon of cinnamon in a small bowl and mix until crumbly.
Spoon the muffin batter into the prepared muffin tin, filling each cup about 2/3 full.
Sprinkle the streusel topping evenly over each muffin.
Bake in the preheated oven for 18-20 minutes or until a toothpick inserted into the center comes out clean.
Allow to cool for a few minutes before transferring to a wire rack.