Preaheat the oven to 350° F (180° C.) Spray an 8x8 (20x20 cm) pan with baking spray or line with parchment paper.
In a large mixing bowl, using an electric mixer, beat the butter, sugar, and brown sugar. Once these are fully combined, mix in the tahini. Next, mix in the egg and the vanilla.
Using a spoon, stir in the flour mixture and the rolled oats until they are only just incorporated. Be careful not to overmix.
Press about 2/3 of the cookie mixture into the prepared pan. Cover it with the chopped chocolate, then the caramel filling. Finally, cover the caramel with pieces of the remaining dough - they should spread out to mostly cover the top during baking.
Bake at 350° F (180° C) for about 24-26 minutes. The tops of the carmelitas will turn a golden brown.
Store at room temperature for up to 3 days, or 4-5 days in the refrigerator.