Melt butter and brown sugar in dutch oven on low heat until sugar is dissolved and starts to bubble. Stir a few times to blend.
Add in vanilla and oats, stir until blended while still heating. Appx 3 to 4 min.
Place half the mixture in bottom of pan and press down firmly.
Melt chips and peanut butter in a micro-safe bowl until blended ( appx 60 sec)
Pour mixture over oats and spread evenly.
Drop remainder of oat mixture over the top . May reserve a little chocolate mixture to dribble over top if desired.
Chill in refrigerator covered for 3 hours .