Preheat oven to 350°F. Line the baking sheets with parchment paper or spray with gluten-free nonstick spray.
In a large bowl, cream the softened butter, brown sugar, and granulated sugar together with a mixer until light and fluffy.
Mix in the eggs until fully combined.
Mix in the baking soda, salt, ground cinnamon, and pure vanilla extract until fully combined.
Mix in the gluten-free peanut butter until fully combined and smooth.
Mix in the gluten-free oats until the batter is well combined. I poured in half of the gluten-free oats at a time. I mixed together and then continued mixing in the rest of the gluten-free oats.
Stir in the M&M's and chocolate chips with a spatula.
Using a greased ice cream scoop, drop the cookie onto the prepared cookie sheets. Take the back of the ice cream scoop and slightly flatten the cookie dough balls. You will have 6 cookie balls per regular-sized baking sheet (9 x 13-inch). If you want to make smaller cookies, use a greased cookie scoop and bake the cookies for 10-12 minutes.
Top the slightly flattened cookie dough balls with a few extra M&M's and chocolate chips.
Bake for 18 minutes for softer cookies and 20 minutes for crisper cookies. Do not overbake.
Cool for 5-10 minutes on the cookie sheets until cookies are set.
Transfer the cookies to a cooling rack to cool completely.
Store leftovers in an airtight container.
For the dairy-free option, I used Smart Balance butter and two cups of Nestle Simply Delicious chocolate chips.
Make sure that your quick oats are gluten-free.
Do not use natural peanut butter. It is too oily for the recipe.
Store in an air-tight container at room temperature.
The cookie dough can be made ahead of time and refrigerated for up to 4 days.
The cookie dough can be frozen for up to 6 months.