Crumbles are not just for fruit!  You can use leftover, cooked  vegetables for this in addition to or in place of the raw vegetables.

3 lbs or so mixed root vegetables, peeled, if necessary, and diced
2 onions, chopped
2 – 3 T butter or olive oil, or a combination
1 1/2 c broth
1 c chopped tomatoes or 2 T tomato paste
1 T grainy mustard, or other prepared mustard
salt and pepper, to taste

Topping:
3 T butter or olive oil
3/4 c ground walnuts, or other nuts
1 1/2 c whole wheat breadcrumbs
1/2 c chopped fresh parsley, or other herb

1. Preheat oven to 350ºF. Melt the butter or heat the oil in a very large skillet. Stir in the vegetables, including the onion, and stir to coat with the butter/oil. Cover and sweat for 10 to 15 minutes, stirring occasionally. Pour in the broth and bring to the boil. Add the chopped tomatoes or tomato paste and mustard. Season with salt and pepper.

2. Transfer to a large baking dish. Put in oven and bake for 30 minutes.

3. Melt butter, if using. In a bowl, combine topping ingredients. Scatter topping over the vegetables and bake for another 20 to 30 minutes until the topping is golden.