Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease it with cooking spray.
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt until well combined.
In another bowl, mix the milk, vegetable oil, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix; a few lumps are okay.
Gently fold in the crushed Oreo cookies and chocolate chips, if using.
Divide the batter evenly among the muffin cups, filling each about ¾ full. If desired, place a whole Oreo cookie on top of each muffin.
Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.