Pre-heat oven to 375 °F (191 °C) and lightly grease a 9-inch cast iron skillet with melted coconut oil. Set aside.
In a medium bowl, whisk together flour, baking powder, and baking soda.
In a large bowl, whisk together granulated and brown sugar. Add the melted coconut oil to the mixture and whisk together. Then add the egg and vanilla extract and whisk until incorporated.
Add the dry mixture to the wet mixture and incorporate together, along with the chocolate chunks, with a spatula or wooden spoon until cookie dough is formed. It will be oily but it's okay.
Press the dough into the pre-greased cast iron skillet into an even layer. If the oil bothers you, you can take a paper towel and dab the grease off.
Bake for 20 minutes or until the edges are golden and crispy.
Remove and let sit for 10 minutes before slicing and serving with a huge helping of ice cream!