Preheat oven to 350 degrees F.
Line two baking sheets with parchment paper.
In a large bowl, beat together butter, brown sugar, and granulated sugar until creamy, about 2 minutes.
Add peanut butter, vanilla, and eggs, and beat again until creamy, about 30 seconds, scraping down the edges as needed.
Add flour, salt and baking soda, beating until combined.
Slowly add in oats, beating until combined.
Stir in M&M's and chocolate chips.
Make approximately ¼ cup sized dough balls and place ~2 inches apart on baking sheets. I got 6 cookies on each baking sheet.
Bake in preheated oven for 11-13 minutes, until edges are golden. They will seem like they are not set up in the middle, but that's okay! They will cool and be deliciously chewy. Just don't overbake them!
Let them cool on the baking sheet for about 5 minutes and then transfer carefully with a spatula to a cooling rack. Let cool completely. Except for that one you have your eye on - eat that one warm with a glass of cold milk.
Repeat with remaining dough.
Enjoy!