I've not tried a savoury crumble, but I think I probably use something like 4 oz wholewheat flour, 2 oz marg and 1 oz rolled porridge oats. If it felt dry whilst rubbing in the marg, then just add some more marg/butter.
For the filling, I'd probably saut� sliced leeks and mushrooms in a little olive oil, add a small amount of flour then some stock and stir well until it thickened up (or use white wine.... ). Pop the veg & sauce into a heatproof dish and top with the crumble mix.... Knowing me, I'd now be adding some parmesan and cayenne pepper to the topping and bake it for about 30-40 mins at Gas 6, 200 deg C.... If I could find a way to add other veg I would so (stuff like sliced celery, chillies, pak choi, garlic and even some fine green beans or other baby veg).