Grease a nine inch square baking pan. Melt butter in a large saucepan over medium heat. Add in brown sugar and vanilla, mix well. Remove from heat and add in the oats. Press half of the mixture in the pan, make sure and spread evenly.
Melt the chocolate chips and peanut butter in the microwave, it only takes about a minute. Pour chocolate mixture over the oat mixture in the pan, spread with a spatula. Crumble the rest of the oat mix over the top of the chocolate and press in gently. (I actually use a potato masher to get it flat) Cover and refrigerate until hard; bring to room temperature to cut into bars, then enjoy!