Mix oatmeal and brown sugar in large bowl and stir to mix well. (Sift brown sugar to remove any lumps). Add melted butter or margarine and stir well to make sure all oatmeal and brown sugar is covered with melted butter.
Pour into a foil covered cookie sheet and press mixture firmly into pan. You may roll it with a rolling pin or glass to press it firmly into the pan. Make sure it is firm and smooth.
Place in 350 degree oven and bake for 10-15 minutes. Check carefully as you do not want the crust to burn. When You see the mixture bubble up it is time to remove from oven and cool thoroughly. This crust must be firm and hard before adding the chocolate mixture.
While crust is cooling melt Peanut butter and chocolate chips in medium pan on low burner. Stir to blend ingredients. Remove pan from stove add sifted powder sugar and stir well to blend.
Pour chocolate mixture over hardened crust and cool until hardened. When cookies are firm and hard lift from cookie sheet with the foil liner and turn out onto foil, wax paper or newspapers. You can break cookies into small to medium pieces. These cookies can be stored in plastic containers or zip lock plastic bags.