Preheat your oven to 350°F and grease an 8x8-inch baking pan. Line with heavy-duty foil or parchment paper, leaving an overhang on two sides to facilitate removal of bars from pan. Grease foil or parchment.
In a medium-size or large bowl, mix the flour, oats, sugar and salt until all ingredients are well-distributed. Stir in the margarine with a fork until well mixed and clumps form.
Press half of the oatmeal mixture into the bottom of your prepared pan to make a thin crust.
Evenly spread the apple butter atop the crust, then sprinkle the remaining oatmeal mixture on top.
Bake until crisp and golden brown, about 30 to 40 minutes.
Let cool completely before using the parchment or foil to remove the bars from the pan in one big piece. Cut into squares.
Recipe by Go Dairy Free at https://www.godairyfree.org/recipes/oatmeal-apple-butter-bars