Preheat oven to 375℉. Grease a standard nonstick muffin tin or line with paper liners.
In a large bowl whisk to combine flour, espresso powder, baking powder, cinnamon, salt, and nutmeg. In a medium bowl whisk to combine milk, bananas, eggs, sugar, oil, and vanilla.
Add milk mixture to flour mixture and stir just to combine. Fold in chocolate.
Divide batter among muffin cups. Bake until a toothpick inserted in the center of a few of the muffins comes out clean or with moist crumbs attached, 15-20 minutes. Let cool in the pan for 5 minutes, then transfer to a rack to cool completely.
For glaze, in a small bowl whisk to combine powdered sugar and espresso powder. Whisk in milk to achieve a pourable but thick glaze.
Drizzle glaze over cooled muffins.