Using a hand mixer or a stand mixer fitted with a paddle attachment, cream the sugars with the butter on medium speed (it will take around 2 minutes). Then at high speed, mix in the egg, the peanut butter, and the vanilla extract (about 2 minutes). Set aside.
Add the flour and the baking soda, and mix on low speed until just combined. Fold in the oats, the M&M's, and chocolate chips.
Preheat oven to 400°F (200°C) and line two large baking sheets with parchment paper or silicone baking mats. Set aside.
Using a medium cookie scoop, scoop out the batter and place on baking sheets. Keep about 2 inches between the cookies as they will spread.
Bake for 8-10 minutes. The cookies will look soft and slightly under-baked. Remove them from the oven and allow them to cool down for 5 minutes.
Transfer to a wire rack to completely cool down.