Assuming that the cowl has gone over the back and not down the intake (logically) and the engine's vital signs are good, keep it running and reduce to minimum practicable speed. Land at the nearest suitable and don't use reverse on that side. Turn it off after rollout and have a visual check for leaks before taking it to the gate.
Take a note of the exact position of the point of cowling departure (if possible) for subsequent recovery.
If nothing hit your flaps / aft surfaces - you are not that badly off at all. Any airframe vibration might well prompt a low speed handling check at a safe altitude. That top cowling support and associated connected panels looks like a candidate for departure so a track away from built up areas - as far as possible - would be worth asking for.
Definately a PAN to get traffic, routing and landing priority - but nothing more drastic.
The PA would prove the biggest challenge.
DG