What is your favourite "crumble mix" topping for fish casseroles?!

I just made a yummy creamy tuna casserole which called for melted butter mixed with weat bix crumbled on top!. I didn't have any weatbix it so I used crumbled Sakata rice crisps instead (no butter)!. It seemed to work (some of the crisps just got crispier, others just sank!. But I was wondering what does everybody use as a favourite savoury crumble mix to go over oven-baked casseroles!? (prefer any without extra oil or butter)Www@FoodAQ@Com

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