In a medium bowl, sift together almond flour, tapioca flour, baking soda, baking powder, and salt. Whisk in old-fashioned rolled oats. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment or a large mixing bowl with a hand mixer, cream the butter and sugars together starting on low speed and increasing to medium-high speed, until light and fluffy, 3-5 minutes. Scrape down the sides.

Mix in the peanut butter followed by the egg and vanilla until just combined, scraping down the sides after each addition.

With the mixer on low speed, slowly add the dry ingredients until just combined. 

Add the chocolate chips and M&M's, mixing until just evenly incorporated.

Scoop generous 2 tablespoon-sized cookie balls onto a parchment-lined baking sheet. I make a heaping scoop using the OXO medium cookie scoop, which is about 45g cookie dough per cookie. For perfectly sized cookies, you can weigh the cookie dough balls on a plate placed on a kitchen scale as you go. Press 4-5 M&M's into the top of each cookie dough ball.

At this point, you can bake immediately or chill the cookie dough in the fridge for at least 20 minutes or the freezer for at least 10 minutes. Unchilled cookies spread a tiny bit more, creating an ever-so-slightly thinner cookie. Chilled cookies spread less, creating a thicker chewier cookie.

When ready to bake, preheat the oven to 350°F. Place the cookie dough balls at least 2 inches apart on a parchment-lined baking sheet and bake for 9-11 minutes for unchilled cookie dough, or 10-12 minutes for chilled cookie dough. Note: Take care not to overbake cookie dough. Pull them out when the edges look set, but the centers still look just a bit underbaked. The cookies will continue baking as they cool. Additionally, the oats will soak up more moisture as they sit. As a result, baking too long will lead to a dry crumbly cookie.

Optional: As soon as the cookies come out of the oven, use a large round cutter or the ring of a large mason jar (larger than the diameter of the cookie) to scoot each cookie into a perfect circle. This method also helps make the centers of the cookie puff up, adding to the thickness and chew factor.

Optional: Gently press candy eyeballs onto each cookie and/or a few chocolate chips. The residual heat from the cookie will melt the bottoms of the eyeballs so they stick and the chocolate chips. Alternatively, you can place some mini chocolate chips on top of the cookies right as they come out of the oven, then wait a few minutes for them to melt before placing the eyeballs on top of the melted chocolate as "glue." Sprinkle with flaky salt, if desired.