Preheat the oven to 200C/400F and line a baking tray with greaseproof paper.
Place the butter and sugar into a bowl and beat on medium until pale and fluffy, approximately 3 minutes with an electric mixer.
Add the egg and continue to beat until well combined, beating for a further minute.
Pour in the tahini and beat until combined.
Add the rolled oats, flour, baking powder, baking soda and salt, beat on low until just combined.
Toss in ⅔’s of the chocolate chunks and stir through.
Scoop a piece of dough and roll the the top of your cookie dough into the remaining ⅓ of chocolate chunks, flattening slightly as you place it on the tray.
Continue scooping and rolling into the chocolate pieces, pressing lightly when you place onto the tray, ensuring there is 1 ½ inches between each cookie.
Place in the oven and bake for 14 minutes until browned on the edges and golden on top.
Remove and allow to cool on the baking tray for a couple minutes before placing on a cooling tray.
Serve with a glass of milk.
Enjoy!