How do I get oat bars (etc) to set??

[flowersinavase]

I've been trying to make bars/finger food for the DCs using porridge oats/dried fruits etc. I bake it all (adding flour and egg) but it never seems to set hard: they always seem to be squidgy in the middle when I take them out (I can't leave them longer or the top would burn).

What am I doing wrong? Too much liquid (so leave out the egg)? Too little flour??

Do you add butter? and syrup? I do and mine tend towards being rock hard.

I'd expect them to come out of the oven soft but hard a bit once they cool?
If they're only squidgy in the middle, could you make them thinner?