Oak leaves are found in salad medlies often with lettuces such as Lollo Rosso (slightly nutty), Lollo Biondi (mild and tender) and Red Oak Leaf (mild and sweet) are grown tightly together in one root ball.
They are often then cut and sold as a three headed lettuce. (source)
So can bearded dragons eat oak leaves?
Yes they can eat oak leaves.
But make sure they don’t eat too much as it will give them bloat if they eat too much.
Just one leaf should suffice for them at any one time so as not to cause them any trouble. They will enjoy them.