Preheat your oven to 400 degrees F. Line your muffin tin with muffin liners.
In a large bowl start by combining the ingredients for the muffin batter. Whisk together the flour, sugar, salt, baking powder and cinnamon. Then add the vegetable oil, egg and milk. Mix together until the ingredients are well mixed.
To this muffin batter add the blueberries and strawberries. Fold the berries into the batter, but don't overmix.
In a small bowl combine the ingredients for the crumb topping. Mix the sugar, flour, cold butter, cinnamon and nutmeg with your hands. Mix the ingredients with your hands until the butter becomes the size of peas and the ingredients are mixed.
Pour the muffin batter into your prepared muffin tin. Add the crumb topping on top of each muffin.
Bake the muffins for 25 minutes or until a toothpick inserted in the center comes out clean.
Allow the muffins to cool for 10-15 minutes before taking them out of the tin and cooling on a drying rack.