Preheat oven to 350. Spray a 9x13 baking dish with cooking spray. Set aside.
In a large bowl, mix oats, flour, brown sugar, salt and softened butter with a spoon. It's easier if you use clean hands, if wanted. Remove a heaping 1 cup and set aside.
Press remaining mixture into the bottom of your prepared pan.
In a sauce pan, combine condensed milk, chocolate chips and 2 tablespoons of butter over medium heat and stir until completely melted and combined.
Pour the chocolate mixture over the bottom layer in the pan and spread evenly. Sprinkle the reserved cup of oat mixture over the chocolate, and top with m&m's. Gently press down.
Bake for 20-25 minutes. Mine are done at 23 minutes.
Let cool completely (about 2 hours) before cutting.