Line a baking sheet with a silicone liner or parchment paper (could also try using non-stick cooking spray).
In a large bowl, combine brownie mix, flour, oil and eggs. Fold in M&M's.
Using a cookie scoop, drop spoonfuls of cookie dough 2 inches apart on baking sheet. Be sure to not flatten cookie before they bake (keep the dough in nice rounded balls).
Bake for 7-10 minutes (if you like your cookies to be a little more done, let them cook longer. To get the chewy, fudgy cookies, keep the bake time around 7-9 minutes).
Remove pan from oven and let cookies cool on baking sheet for 3-5 minutes, then transfer to a wire rack to let them cool completely.