Prep the oven. Heat oven to 375°F. Line a 12-cup muffin tin with paper liners.
Blend. Combine the spinach, bananas, maple syrup, milk, oil and vanilla in a blender. Pulse until smooth. Add the remaining ingredients and pulse until just combined, pausing to stir the ingredients and scrape the sides of the blender if needed.
Bake. Pour the batter out evenly into the 12 muffin cups (they should be nearly full). Bake for 14-17 minutes or until a toothpick inserted in the center of a muffin comes out clean.
Serve. Transfer the pan to a wire rack and let the muffins cool for at least 10 minutes. Or let the muffins cool to room temperature, then store in a sealed container for up to 3 days, or freeze for up to 3 months. Serve and enjoy!