Preheat oven to 200c
Heat them oil in a large heavy oven proof casserole, add the sausages and fry gently for 2-3 minutes until golden, turning them occasionally.
Add the onions, half the garlic, carrots, and thyme, cook for 5 minutes.
Add the tomatoes, tomato puree, drained cannellini beans, and mix well.
Add the stock and bring to the boil, scatter over the 3 grains, cover casserole dish with a lid, place in the oven for 15-20 minutes.
Meanwhile mix the breadcrumbs, remaining garlic, mustard, and parsley in a bowl.
Remove casserole from the oven, carefully remove lid, sprinkle the breadcrumb mix evenly over the top of the sausages and return to the oven for 5-8 minutes until the crumbs become golden and bubbling (alternatively you can place the dish under a hot grill).
Serve direct from the oven.