Packed lunch ideas with protein for restricted eater

[SprigatitoYouAndIKnow]

Ds2 is very difficult to make packed lunch for. He will eat a limited number of mains, so it is fine at home, but they all require cooking. They wouldn't be things we could keep warm until lunch either eg scrambled egg, super noodles, pizza. He likes a food until he goes off it. We recently lost tuna wraps, so have no idea what to give for lunch at school. Awaiting autism assessment, so this is not just average picky eating.

He currently has a bread roll that comes back vaguely nibbled, fruit and veg, yoghurt fruits type thing and a snack bar suck as a penguin. He is fine with peanut, but school ban that due to kids with severe allergies. It means he comes out of school starving and in a big ball of rage.

I am thinking of swapping the snack bar for a homemade muffin or cookie. Does anyone have recipes for making these high protein and suitable for children? All the recipes I can find seem to be for gym bunnies and are packed with protein powder and artificial sweetener.

https://minimalistbaker.com/vegan-gluten-free-black-bean-brownies/

@orpmoa I love the idea of making protein brownies in muffin trays. Much easier to portion amd freeze.

@BoudiccaOfSuburbia filling is what I am trying to get to. There are so many things he won't touch and then he comes out starving and yelling at me for food. He eats most fruit and veg, which is great, just burns off quickly.

@AlltheFs no pasta sadly. All the things that everyone knows kids love are usually refused. Except for pizza.

@Another2Cats he used to eat smoked salmon, but that's gone now. He will eat fish fingers or battered fish with the coating removed, but only hot. I think because they are more uniform than less processed fish that might look different every time.