Line cookie sheets with waxed paper. In large saucepan, combine brownie mix, milk and butter. Cook over medium heat until mixture comes to boil, stirring constantly. Boil 2 minutes, stirring constantly. Remove from heat.
Add peanut butter and vanilla, blend well. Stir in oats. Carefully fold in M&Ms.
Drop dough by tablespoonfull onto the cookie sheets. Let cool until set.