Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners or lightly grease it.
In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt until evenly combined. The mixture should look like a uniform dry blend.
In a separate bowl, beat the eggs, then stir in the vegetable oil and vanilla extract until smooth and slightly frothy.
Pour the wet mixture into the dry ingredients and gently fold with a spatula until just combined. Do not overmix; the batter will be thick.
Fold in the chopped spinach, distributing it evenly throughout the batter. You should see bits of green throughout the mixture.
Gently fold in the chocolate chips, being careful not to deflate the batter too much.
Spoon the batter into the prepared muffin tin, filling each cup about three-quarters full. Tap the tin gently to level the batter and remove air bubbles.
Bake in the preheated oven for about 18–20 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. The muffins should be firm on top and slightly glossy.
Remove the muffins from the oven and let them cool in the tin for 5 minutes, then transfer to a wire rack to cool completely. They will be moist and tender with a crackly cocoa crust.
Once cooled, serve these vibrant green-speckled muffins warm or at room temperature for a soft, moist, and chocolatey bite.
