Preheat oven to 350 F. Grease a 9 x 13 pan and set aside.
In a large bowl, cream together butter and brown sugar. Beat in peanut butter, eggs and vanilla.
In a separate bowl, stir together flour, and baking soda. Add to large bowl and stir until combined. Add oats, chocolate chips and M&Ms.
Press into greased pan. Add additional M&Ms to the top, if desired, pressing them into the dough slightly.
Bake for 14 - 16 minutes or until edges are slightly brown or until toothpick inserted comes out clean. Do not over bake. Let cool a bit before slicing. Letting them cool completely is best. But its almost impossible to wait that long.
Notes
I use salted butter to make this recipe. If you prefer to use unsalted butter, you might want to add a pinch of salt to this recipe.