Preheat oven to 350?F (175?C). Line an 8x8-inch pan with parchment paper. Let eggs come to room temperature.

Thaw spinach completely, then squeeze out all excess moisture. Blend spinach with applesauce and Greek yogurt until smooth. Set aside.

In a large bowl, whisk cocoa powder, flour, salt, baking powder, brown sugar, and white sugar together.

In a separate bowl, beat eggs with vanilla. Slowly whisk in melted coconut oil, then add spinach mixture. Mix until smooth.

Gently fold dry ingredients into wet mixture until just combined. Stir in chocolate chips, nuts, or any optional add-ins.

Pour batter into the prepared pan. Smooth the top and bake for 25-30 minutes. Let cool completely before cutting into squares.