Cook 1 chopped onion, add 4 peeled and diced tomatoes. Also add thyme to taste and season it. Cook 400g green beans until just done. Drain and transfer to an baking dish. Pour over the tomato sauce. Then make a white sauce. Melt 30g butter and add 30g plain flour. Gradually add 150ml vegetable stock and 150ml milk and boil for 3 minutes. When the sauce is ready pour over the green beans. Scatter some grated cheese and some bread crumbs over the dish. Place the baking dish in a preheated oven at 200c for about 20 minutes. Enjoy!