Preheat oven to 350.
In a large mixing bowl, cream together softened butter and brown sugar.
Using a hand mixer on medium speed, beat in peanut butter, eggs, and vanilla.
In a separate bowl, mix together flour, baking soda, and salt. Mix in oats.
Pour into large bowl of wet ingredients and mix well on medium speed.
Fold in M&M's and chocolate chips with a spoon.
Press batter into a greased 9x13 pan.
Bake for 15 minutes or until toothpick comes out clean.
Cool completely and cut into squares