Salad nicoise is good for picking at. It's cooked green beans left to go cold. Add quartered hard boiled eggs, anchovies, olives, croutons, lettuce. Google a recipe in case the one above isn't quite correct.
I like cold lasagne but I think that's already been suggested.
I used to go to two evening classes on a Monday night. The second one was a forty minute drive from home. I used to make chilli con carne, leave it to go cold, cook some rice and when that had gone cold I mixed them together. It was tasty, not perfect but it meant I didn't go hungry.
Same deal with pasta Bolognese. Cook some pasta shapes i.e. quills or shells leave them to go cold and mix into the cold sauce. I used to put mine in a freezer bag as the seal did not leak then eat it out of the freezer bag with a spoon in the car outside of the first evening class before driving to the next evening class.
I also made a curry, and cooked the rice. Left both to go cold, mix them together, put it in a zip lock freezer bag then eat it out of the bag with a spoon.
I've made frittatas before now. Breakfast frittatas I called them. They had bacon and mushroom in them. We were driving a long distance and wanted to stop somewhere at our convenience, not either to early or to late dependent on whether we could stop in a town and would they still be open ?
Make up a snack box of cubes of maybe, cheese, chunks of cucumber and carrot, grapes, apple, pineapple, tomato, raisins, kidney beans maybe quarters of hard boiled egg so he can just pick at these as the day goes by.
Would he eat tinned ravioli cold straight from the tin ? Or soup straight from the tin ? I've done this when there's been no microwave and no staff rest area at work.