Preheat oven to 375°F. Fill cupcake tin with paper liners.
In a small bowl, mash 1/2 cup of the strawberries with a fork. Set aside.
In a medium bowl, combine the oil, milk, egg, and vanilla extract. Lightly beat together.
In a large mixing bowl, combine the flour, baking powder, sugar, and salt. Add in the remaining chopped strawberries and stir gently to coat; then fold in the mashed strawberries.
Slowly pour the milk mixture into the bowl with the dry ingredients and fold the ingredients together using a spatula. Mix just until the ingredients are incorporated, but do not over mix.
Fill each liner 3/4 of the way full with strawberry muffin batter.
In a small bowl, combine the sugar, flour and cubed butter for the streusel topping. Mix with a fork, breaking down the butter, until it starts to resemble crumbles.
Sprinkle the streusel topping over each filled cupcake tin.
Bake for 20 minutes until muffins have risen and the tops are light brown.