Preheat oven to 350 degrees. Line a 9x9 baking pan with parchment paper.
In a microwave safe bowl, melt ½ C chocolate chips on 50% power for 2 minutes, then stir every 30 seconds until melted. Add the coconut oil to the melted chocolate and stir well. Add in the tahini and vanilla and stir until smooth. Set aside to cool a bit.
In a large bowl, sift together flour, cocoa powder, salt and baking powder. Stir in sugars. Add the melted chocolate mixture to the flour and fold together.
In a smaller bowl, crack the eggs. Beat the eggs. Add the beaten eggs to the chocolate mixture. Fold together until mostly smooth (there may be a few small lumps). Fold in the other ½ C chocolate chips. Spread into prepared pan.
Combine the swirl ingredients in a small bowl. Stir well until smooth. Dollop tahini on top of brownies. Then swirl around with a knife or wooden skewer.
Bake in preheated oven for 25-28 minutes, until toothpick inserted comes out with just a few crumbs attached.
Remove from oven and cool in the pan. Store in an airtight container.