Preheat oven to 400°F. Coat a 12-cup muffin tin with cooking spray.
Combine 1 cup milk and 1 tablespoon lemon juice in a medium bowl. Set aside.
Whisk 1 cup each oats and flour, ½ cup brown sugar, 1 teaspoon baking powder, ½ teaspoon baking soda and ¼ teaspoon salt together in a large bowl.
Whisk egg, ¼ cup oil and 1 teaspoon vanilla together in a medium bowl. Add the milk mixture and combine. Add the wet mixture to the dry mixture; stir until just moistened. Gently fold in 1 cup raspberries.
Divide the batter among the prepared muffin cups. Bake until a toothpick inserted in the center comes out clean, 15 to 22 minutes. Let cool in the pan for 10 minutes before transferring to a wire rack.
