Something I do with my own kids is that I keep a container of cut up veggies in the fridge and if they are hungry at non meal/snack times, they can have some of those. If figure if they are truly hungry, they will eat the veggies. They love veggies.

You could do the same and serve it with some hummus (protein!) to dip them in.

Or maybe keep some hard boiled eggs in the fridge?