Three Bean Crumble- vegan

I was thinking about an alternative to my usual pasta bake in cheese or tahini sauce when I had this idea. I love taking a type of dish (eg: crumble, cake) and changing it from sweet to savoury and vice-versa! If you use cornflour instead of wheat flour in the sauce and buy oats which have not been milled in contact with wheat, it will be wheat-free and gluten free too. This recipe serves 6-8 people.
Filling:
1kg cooked mixed beans (I used butterbeans, red kidney beans and blackeyed beans
1 small sweet potato, sliced/ diced
1 med parsnip, diced
3-4 sticks of celery
50g fine green beans, sliced
50g broccoli, cut into small florets

• Sweat the vegetables in a little oil until just tender
• Remove from heat, stir in the beans and put into an ovenproof dish

Sauce for filling:
2 tabs oil (organic sunflower oil is good)
1 tab yeast extract
2 heaped tabs plain flour
1 l soya milk
1 tsp salt
1 tab tahini
Make a roux by mixing the yeast extract, flour and oil over a gentle heat

• Mix in the soya milk gradually with a balloon whisk
• When the sauce begins to thicken, remove from heat and stir in the tahini
• Pour over the vegetables and beans in the baking dish.

Crumble topping:
200g porridge oats
100g sunflower seeds
100g buckwheat flour
Water to mix 

• Combine dry ingredients
• Mix to crumble consistency with a little water
• Scatter on top of the beans, vegetables and sauce

Bake the crumble at 200C  (or maybe 220C if you don't have a fan-assisted oven) for about 30 mins, or until the top is crispy and starting to brown.