Preheat the oven to 375°F (190°C). Line a muffin tin with paper liners or grease with butter or oil.
In a large bowl, mash the bananas with a fork. Add lemon juice, melted butter or coconut oil, Greek yogurt, milk, and eggs. Mix well.
In another bowl, combine gluten-free flour blend, almond flour, brown sugar, baking powder, baking soda, xanthan gum, and salt.
Add the wet ingredients to the dry ingredients and mix until just combined.
Fold in ¾ of the chocolate chips, reserving some to sprinkle on top of the muffins.
Fill each muffin cup to the brim with batter.
Sprinkle the reserved chocolate chips on top of the batter in each muffin cup. Bake for 20-25 minutes or until a toothpick inserted into the center comes out clean.
Let the muffins cool n the tin for 5 minutes, then transfer to a wire rack to cool completely.
