Preheat the Oven
Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease it.

Blend Banana and Spinach
In a blender, combine the bananas, baby spinach, and milk. Blend until smooth and bright green.

Mix Wet Ingredients
Pour the blended mixture into a large bowl. Add the egg, sugar, vanilla extract, Greek yogurt, and oil. Stir until well combined.

Add Dry Ingredients
Add the flour, baking soda, cocoa powder, and sea salt. Mix gently until the batter is smooth.

Fold in Chocolate Chips
Stir in the dark chocolate chips, reserving a few to sprinkle on top if desired.

Fill Muffin Cups
Divide the batter evenly among the muffin cups, filling each about 3/4 full.

Bake the Muffins
Bake for 18–22 minutes, or until a toothpick inserted in the center comes out mostly clean.

Cool and Serve
Allow the muffins to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.