Preheat oven to 350 degrees. Cut a strip a parchment paper to fit the bottom of a 9×13 pan, but hang over 2 of the edges. Spray pan with non-stick spray and then place parchment in, pressing paper to spray to help it stick. (Alternately you could line with foil and lightly spray with cooking spray.) Set aside.
Place oats in your blender and pulse just a couple times to barely break up oats. You don’t want to create oat flour! They should still look like oats, just broken up a little into smaller pieces. Set these aside.
Combine flour, baking soda, and salt in a bowl and lightly whisk to combine. Set aside.
In a mixing bowl or stand mixer, melted butter, brown sugar, and white sugar. Add eggs, one at a time, stirring between each addition, and vanilla. Add flour mixture in a couple additions until incorporated.
Stir in oats and chocolate chips until just combined. *I like to just sprinkle my M&M’s on the top of the dough, but if you have a big bag, feel free to toss a small handful into the dough, or substitute M&M’s for a portion of your chocolate chips.
Press dough into prepared pan and press flat. Sprinkle a handful of M&M’s on top and add sprinkles if you desire.
Bake for about 25-30 minutes. Remove from oven when edges are golden brown and center appears set, but still soft. The center should jiggle a bit when you move the pan. They will be very doughy in the middle! Unless you are serving slightly warm over ice cream, cool completely to room temperature. Note: It’s totally normal for the center to sink down lower than the edges, once cooled! I think these are best when they’ve cooled for several hours and I like to put them in the fridge to chill before cutting, even. They are great to make ahead!