Fudge Filled Bars

2 cups quick-cooking oats
1 1/2 cups all-purpose flour
1 cup packed brown sugar
3/4 teaspoon salt
1 cup butter or margarine melted
1 cup chopped pecans optional--I usually don't use anymore as so many people are allergic to different kinds of nuts.
1 can 14 ounces sweetened condensed milk
1 cup 6 ounces semisweet chocolate chips
2 tablespoons shortening
1 cup plain M & M's