In a large bowl combine the oats, flour, brown sugar, and salt. Add the melted butter and mix until crumbly. Set aside 1 1/2 cups of mixture for the topping. Press remaining crumb mixture into a greased 9 x 13-inch baking pan.

In a small saucepan combine the sweetened condensed milk, chocolate chips, and shortening. Cook and stir over medium-low heat until the mixture is melted together and smooth.

Evenly spread the chocolate mixture over the crust and sprinkle with the reserved crumb topping. Evenly distribute M&M's over the top, gently pressing the candies into the crumb mixture. Bake at 350° for about 25 minutes or until edges are golden and center is set.