Sift the flour, salt, and baking soda into a medium bowl then add the oats, whisk together and set aside.
Cream the butter and peanut butter together then scrape the bowl down and beat in both sugars; beat on medium speed until light and fluffy.
Reduce speed to low; add the vanilla and eggs. Beat until well mixed, about 1 minute.
Add flour mixture; mix until just combined.
Stir in the M&Ms and chocolate chips. Cover and chill dough for at least 20 minutes to overnight.
Preheat oven to 350 degrees. Roll 2 tablespoon-size balls of dough in your clean hands and place about 2 inches apart on baking sheets lined with parchment paper. For a prettier cookie you can press a few chocolate chips and M&Ms on top of each cookie before baking.
Bake until cookies are golden around the edges, but still soft in the center, 10 to 15 minutes. The longer bake time will give you a crisper cookie.
Remove from oven, and let cool on baking sheet 1 to 2 minutes. Transfer to a wire rack, and let cool completely.
A generous sprinkle of sea salt on top makes takes these cookies to a whole new level. Use a large flake sea salt like Malden's if you can find it.Use a thicker peanut butter for best results. If you have a natural brand with a separated layer of oil on top pour it off (saving it for later) and use the thicker part of the mixture. You can add bits of toasted peanuts to this recipe for extra crunch is desired. I recommend about 1/2-3/4 cup.