Preheat the oven to 350 degrees F. Line a large sheet pan with parchment paper or a Silpat liner and set aside.
In a large bowl, stir together the flour, oats, brown sugar, baking soda, and salt.
Melt the butter and allow it to cool to room temperature, so it doesn't melt the sugar and cause greasy cookies. Combine with the vanilla extract and egg. Pour into the dry ingredients.
Stir everything together until a thick dough forms. You may need to knead the mixture with your hands.
Cover and refrigerate the dough while you unwrap the Rolos.
Flatten the dough in your hand (about 2.5 to 3 tablespoons of dough) and press two candies into the center of the cookie. Press the edges up around the candies and completely seal into a large cookie -- the dough should just cover the Rolos without much extra. Make sure none of the candies are exposed or the caramel will leak out during baking.
Place 6 - 8 cookies on the prepared sheet pan, giving the cookies plenty of room. Refrigerate the tray for 10 minutes to firm up before baking.
Bake for 9-12 minutes. Slightly underbaking these is the BEST! It creates a softer cookie with melted and gooey caramel. Overbaking makes the caramel harden when cooled.
I remove the cookies generally at 9-10 minutes, allow them to sit on the cookie sheet for another 2-3 minutes, and then transfer to a cooling rack to allow them to firm up a bit.
To top with chocolate, combine the chocolate chips and vegetable oil in a microwave-safe bowl. Microwave for 30 seconds, stir for 15 seconds, and then microwave again in bursts of 15 seconds, stirring in between each burst for 10 seconds until completely melted.
Dip a spoon in the melted chocolate. Run the spoon from left to right over the cookies to get the chocolate drizzle. Alternatively transfer the chocolate to a small plastic bag, snip off the top with scissors, and drizzle all over. Let stand.
Cookies best enjoyed within 1-2 days of making; best on the same day they're made!