Mix oatmeal, flour, butter, brown sugar, baking soda and salt. Reserve 1 1/2 cups for topping. Grease a 9 x 13 pan. Put the rest of the mixture in the pan and pat down. Bake for 10 minutes at 350°.
Heat oil in a small pan on the stove. Add 1/2 pound of M&Ms. Give the M&Ms a couple of minutes to heat up then smash them with a potato masher until broken. Take off the stove and add the can of sweetened condensed milk and mix.
Pour over baked crust. Then sprinkle on the 1 1/2 cup of reserved topping and the remaining 1/2 pound of M&Ms. Bake and additional 18 minutes. Cool and cut.