Preheat the oven to 350°F. Line baking sheets with parchment paper. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and peanut butter on medium-high speed until smooth, about 1-2 minutes.
Add brown sugar and mix on medium-high speed until smooth.
Add eggs, scraping down the sides of the bowl as needed.
With the mixer off, add the flour, oats, baking soda, and salt. Mix on low until just combined, being careful not to overmix.
Mix in the M&M's and chocolate chips.
Reserve 1 ½ cups of the cookie dough.
With the remaining cookie dough, drop 1 tablespoon of dough onto the lined baking sheets about 2 inches apart. Top with mini M&M's (optional).
Bake the cookies for 10 minutes, or until the sides are lightly browned and the centers still look soft.
Remove from the oven and let cookies cool on the baking sheet for a few minutes before transferring to a wire rack to finish cooling. Reserve the cookies for topping the cheesecake.
Line a 7-inch springform pan with parchment paper, including up the sides.
Press the reserved cookie dough into the bottom and halfway up the sides of a lined springform pan. Set aside.