Rinse the beans well. Trim the edges of the beans and chop them each of 1 inch long.
Add the chopped beans to a sauce pan along with water till immersing level. Add salt to it.
Cook until aldente. Drain water and set aside. You can add this reserved water while making white sauce.
Heat oil in a kadai, add onion and capsicum. Sauté till until the onions turn golden, set aside.
Heat butter in a pan, add flour. Sauté for a minute then add milk, add drained water also. Let it boil for few mins.
Add oregano, pepper powder and salt. If you want you can add cheese in white sauce too. Cook until the sauce is thick and coats the ladle.
Now add cooked beans, sautéed onion capsicum. Toss well.
Transfer this to a casserole dish. Sprinkle breadcrumbs over it.
Meanwhile preheat oven at 200 deg C for 10 mins.
Finally sprinkle cheese and bake in preheated oven at the same temperature for 25 mins or until the top turns golden.
Serve Green Bean Casserole hot!