Chop the onion and fry in a little olive oil until lightly golden.
In a medium pot, add peeled potatoes (whole), cover with water and boil until tender then remove them from the water with a slotted spoon. Either mash or pass through a potato ricer into the bowl containing the cooked onion.
Clean and trim the green beans. Cut into small size pieces and set aside. Once the potatoes are cooked, remove them from the water, add the chopped green beans to the same water, and cook just until tender.
Add the eggs and beat with a fork, then add the parmesan cheese, oregano, salt and pepper, and combine. Then add to the large bowl and gently combine all the ingredients.
Spoon into the prepared baking dish, sprinkle with remaining 2 tablespoons of bread crumbs, dot with 1 tablespoon of butter and bake.