Preheat your oven to 350°F (175°C).
Prepare your muffin tin by lining it with paper liners or greasing it.
In a bowl, whisk together baking powder, baking soda, salt, and ground cinnamon.
Combine rolled oats and almond milk in a large bowl and let sit for 10 minutes. Then stir in maple syrup, melted coconut oil, and vanilla extract.
Gradually add the dry mixture to the wet ingredients and stir gently until just combined.
Fold in cranberries and walnuts if using.
Divide the batter among muffin cups, filling each about 3/4 full. Bake for 18-20 minutes until a toothpick comes out clean.
Let cool in the pan for 5 minutes before transferring to a wire rack.