Preheat the oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper.
In a large bowl, whisk the Greek yogurt, eggs, melted butter, monk fruit sweetener and vanilla until smooth.
Add the cocoa powder, flour, baking powder and salt. Fold just until combined, then spread the batter evenly into the pan.
Bake for 20-22 minutes, until the top is set and a toothpick inserted in the center comes out with moist crumbs.
Remove the pan from the oven and scatter the mini marshmallows, graham cracker pieces and mini chocolate chips evenly over the top.
Return to the oven for 3-4 minutes until the marshmallows are puffed and soft. For golden toasted tops, switch the oven to broil for 30-60 seconds, watching the whole time because marshmallows go from golden to burnt very fast.
Cool in the pan for at least 30 minutes so the marshmallow sets, then cut into 16 squares.
