That's a great strategy from your doctor -- in fact, frozen peas were suggested to me when I had oral surgery because the bag conforms to your facial features better than a regular ice pack would. 😀 Have you tried looking on Amazon at some of the ice cap/hat/beanie options? It would probably be a bit more practical than the lentil method, especially if you're doing it regularly.
Looking forward to hearing your thoughts once you find something worth buying! Amanda lists a couple products in this article she wrote a while back:
https://migraine.com/living-migraine/headache-hat-experience
Good luck, both of you! -Melissa, migraine.com team