Slow release energy/ protein snack/ bar recipe ideas?

[UntilYourNextHairBrainedScheme]

My 14 year old is having a massive seemingly endless growth spurt, plays a lot of sport and dislikes eating anything meal like close to training as it makes him feel sick. He's started getting really debilitating migranes after football training - it happened once, then not for a couple of weeks, then last week and again today. I'm sure its partly blood sugar.

Any ideas for tray bake protein bar type things without buying protein powder (I'd rather use "real" ingredients if possible) and without coconut (simply because he doesn't like it)? No allergies, peanuts are fine - I'm thinking peanut butter will play a role?

I love making these in batches and freezing some. The coconut is optional.
Cheese and marmite flapjacks are popular with my dc at the moment.

Fivemoreminutes1 thanks for those - the first ones look perfect (as you say the coconut is optional so can be left out).