Do I need to use oat flour in this recipe?

No, you can use all-purpose or 1:1 gluten-free flour if you don’t have oat flour. You can also blend quick oats until they are a flour-like consistency.

Can I leave out the protein powder?

You most certainly can. If you don’t want to add protein, you still need to maintain a similar wet/dry ratio of ingredients. So, just replace with the same amount of flour. One scoop of protein powder is about 1/4 cup of flour.

Are these macro friendly slutty brownies best warm or chilled?

I personally love eating these brownies chilled! I think the flavors really come together but you can absolutely eat them warm if you prefer. Just pop them in the microwave for a few seconds until warmed to your liking.