Preheat the oven to 350°F. Line a muffin tin with silicone or parchment paper liners and set aside.
Add the Greek yogurt, eggs, maple syrup, olive oil, milk, and vanilla to a large bowl, whisk to combine.
To the same bowl, add the flour (make sure to do this first), cocoa powder, chocolate chips, then sprinkle the baking powder, baking soda, salt, and espresso powder if using, evenly over the top. Mix until just combined, being careful not to overmix.
Divide the batter evenly between the lined muffin cups, filling them about ¾ full. Let the batter rest for 10 minutes before baking. Top with additional chocolate chips if desired.
Bake for 22-24 minutes, or until the muffins are set and a toothpick inserted into the middle comes out mostly clean with a few moist crumbs.
Cool in the pan for 10 minutes, then transfer to a rack to finish cooling completely.
