Preheat Oven: Preheat the oven to 350℉ and line two baking sheets with parchment paper.
Combine Dry Ingredients: In a small bowl, mix the flour, oats, and baking soda until well-combined.
Cream Butter and Sugar: In a large bowl, use a hand or stand mixer to cream together the butter and sugars until light and fluffy.
Add Peanut Butter, Egg, and Vanilla: Add the peanut butter and mix until well combined. Then add in the egg and vanilla mixing throughly.
Add Dry Ingredients: Pour in the flour and oat mixture. Mix on low until the dry ingredients are fully incorporated.
Stir in Add-In's: Gently fold in the M&M's and mini chocolate chips until they are evenly distributed.
Scoop: Using a large (3-tablespoon) cookie scoop or a scant 1/4 cup, portion the cookies and place them on the prepared sheets. about 3 inches apart.
Bake: Bake the cookies for about 20 minutes, until they are crisp and light golden brown on the edges. Rotate the pans halfway through baking. Remove from the oven and let cool on the pan for 5 minutes before transferring to a cooling rack.