First, I know that this one isn't as quick as some others, sorry! You may know this, but a lot of regular brownie boxes now have reduced-fat recipes printed in very small print on the box. The brand I just used actually has a "Low fat" box that tells you to make the recipe with the same directions as the "traditional" box's reduced-fat ones. And they end up with basically the same nutrition info. Funny, isn't it? Well, for my box I ended up with 3 grams of fat per serving instead of 9, and that made me much happier about sharing them with friends over the weekend. When you can get the box for around $1, this is definitely a good, cheap option.
In case you can't find the healthier directions, these are the changes on my box.
Pour mix into bowl.
Add 1 tablespoon less water than original recipe.
Add 1 egg (original asked for two.)
Add applesauce, mashed banana, or plain non-fat yogurt equal to the amount of oil called for.
Bake in a pan - may take a few minutes less than the traditional recipe.