1cupsemisweet chocolate chips(can substitute white chocolate or milk chocolate chips)
Preheat oven to 350°F. Line 2 baking sheets with parchment paper or silpat baking sheets.
In a large bowl, combine flour, oats, cocoa powder, salt, baking soda and baking powder. Set aside.
In the bowl of a stand mixer, add butter, yogurt and banana. Mix with paddle attachment until smooth. Add granulated sugar and brown sugar and mix until combined (may look curdled–no big deal!). Add eggs and vanilla; mix well. If you don't have a stand mixer, you can use a hand mixer.
With the mixer on low, gradually add dry ingredients. Mix until just combined. If you're using a hand mixer, stir in the dry ingredients by hand. Mix in chocolate chips and walnuts by hand.
Using a large cookie scoop (about ¼ cup), scoop batter onto prepared sheet pans about 2 inches apart. Bake for 13 to 15 minutes or until set. Cool completely on baking sheets before storing in an airtight container.