Preheat the oven to 350°F. Spray a 13"x18" sheet pan (or 2 9"x13" pans) with cooking spray until the bottom and sides are all covered
Pour your brownie mix (1 box) into a large bowl and add the eggs (2 eggs), vegetable oil (½ cup), water (3 tablespoons), and peppermint extract (1 teaspoon). Slowly mix with a whisk until everything is combined and you can't see any streaks of egg or brownie mix anymore
Pour the batter into your prepared pan, and use a rubber spatula to spread it in an even layer across the whole pan. Make sure to get enough batter in the corners, too!
Bake for 10 minutes, then turn your pan 180° and return to the oven. Your batter should look something like this when you turn it. Bake for 10 more minutes
While the batter is in the oven, put the chocolate chips (½ cup) in a small microwave safe bowl or mug. Microwave for 30 seconds, then take them out and stir them. They'll look like they're barely starting to melt, but you want to stir chocolate chips frequently while melting to evenly distribute the heat
Continue to microwave in 15 second intervals until the chocolate is fully melted
To make the chocolate easier to drizzle, you can add 1 teaspoon of vegetable oil to your melted chocolate and stir it well. This step is optional
Remove the brownies from the oven
While they brownies are still warm, drizzle with chocolate and cut into squares. Since these brownie thins are pretty brittle, they are much easier to cut while they're warm than once they cool off