Preheat oven to 350 degrees F. Have one or two large rimmed baking sheets lined with parchment paper.
With an electric mixer, beat the butter and all sugars until blended. Add eggs one at a time and beat on medium until pale and fluffy. Add vanilla, corn syrup and peanut butter and mix until smooth.
Beat in the baking soda, then beat in the salt ONLY if you used unsalted butter.
Add oats one cup at a time, mixing well. Stir in the chocolate chips and M&Ms mixing until completely incorporated.
Using a heaping 1/3 cup measure or a more level ½ cup, scoop out large chunks of dough. Each should weigh around 4 ½ oz. Shape into firm balls and press tops to make mounds.
Arrange about 5 to a baking sheet and bake one sheet at a time for 15 minutes. Scoop onto baking sheet using a serving spoon or small ice cream scoop. Bake at 350 degrees for 15 minutes. Enjoy!