Preheat oven to 375°F. Spray a muffin tin with cooking spray or use silicone muffin cups.
In a large bowl, whisk together the yogurt and milk until smooth. Stir in the oats. Allow oats to soak for 10-15 minutes.
When done soaking, stir the oil, eggs, mashed banana, maple syrup, lemon zest and vanilla extract into the oat mixture.
In a large mixing bowl, combine the flour, baking powder, baking soda, and cinnamon.
Add the dry ingredients to the wet ingredients and stir to combine, being careful not to over mix.
Gently fold in the blackberries, reserving some to press into the surface of the muffins.
Divide batter evenly between twelve cups in the muffin pan. Press the reserved blackberries into the top of each muffin. Bake for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool for 5-10 minutes before transferring to a wire rack to cool completely.