Preheat oven to 325ºF. Spray a muffin tin with cooking spray and set aside.
In a large mixing bowl, combine the dry ingredients: flour, Truvia (or sugar), cocoa, baking soda, salt, and chocolate chips.
In another mixing bowl, mash avocado with fork. Whisk in yogurt.
Measure out milk, oil and vanilla and pour into avocado/yogurt mixture. Whisk together.
Combine the flour mixture and avocado mixture until incorporated.
Scoop into prepared pan, filling about 3/4 full. Top each muffin with a sprinkle of chocolate chips, if desired. Place in preheated oven and bake for about 35 mins, until toothpick comes out mostly clean and muffins spring back when touched.
Let cool and then careful extract from muffin tin and enjoy!