Preheat oven to 350 degrees. Prepare a cookie sheet by lining with parchment paper.

 In the bowl of a mixer, combine butter, brown sugar, sugar, and peanut butter. Mix until fluffy and pale in color. About 1-2 minutes.

Add the eggs and vanilla extract. Mix together.

Add in the oats and baking soda. Mix until combined.

Add in the m&m's and chocolate chips (reserve some for top of bars if wanted). Stir together until combined.

Pour dough onto the cookie sheet and spread out evenly. Sprinkle the reserved m&m's and chocolate chips on top (if wanted). Press down slightly into dough.

Bake at 350 degress for 17-20 minutes. The edges will be lightly browned and the middle will still look pale and underdone, but it will finish baking as it cools. Allow to cool for at least an hour.