Preheat oven to 350℉ and line 14-18 muffin tins with paper cups.
In a medium bowl, whisk together flour, cocoa, baking soda, baking powder, and salt.
In a large bowl, whisk together sugar and oil. Add eggs one at a time, whisking well after each. Peel and mash bananas, add to bowl along with yogurt, orange juice and vanilla. Whisk to combine well, then add flour mixture, whisking until just combined and starting to smooth out. Stir in chocolate chips.
For large muffins, scoop a generous 1/3 cup of batter per muffin tin. For smaller muffins, use a 1/4 cup of batter per muffin tin.
Bake in preheated oven for 18-20 minutes, depending on size. Remove from oven and allow to cool in pan slightly before moving to a cooling rack to cool completely.
Will keep for several days at room temperature wrapped individually or in a sealed container. They freeze well wrapped individually and will keep for up to a month.