Preheat the oven to 350℉. Line a baking sheet with parchment or a silicon mat.
In the bowl of an electric mixer fitted with a paddle, cream together the butter, sugar, and peanut butter until fluffy, about 3-4 minutes. Add the egg and vanilla and continue to mix, scraping the sides as needed.
½ cup unsalted butter, 1 cup light brown sugar, ¾ cup creamy peanut butter, 1 large egg, 2 teaspoon vanilla extract
In a separate bowl, combine the baking soda, flour, and salt and stir to mix. With the speed on low, slowly add the dry ingredients to the bowl and mix until just combined. Do not overmix. Add the oats, M&Ms, and chocolate chips and mix until just combined.
1 teaspoon baking soda, 1 ¼ cups all-purpose flour, ½ teaspoon kosher salt, ½ cup quick oats, ¾ cup M&Ms, ½ cup bittersweet chocolate chips
Spoon 2 tablespoon portions of dough onto the prepared baking sheet, leaving 2-inches in between each one. Bake for 11-13 minutes or until the edges are golden brown. Gently press down on the top of each cookie with the back of a spoon to flatten. Allow to cool on the baking sheet for 10 minutes. Transfer the cookies to a wire rack to finish cooling.