Heat olive oil in a medium sauce pot over medium-high heat. Add onions and a sprinkle of salt and pepper. Saute until tender, about 6-7 minutes.
Add in green beans, tomatoes, salt and pepper to the pot and stir to combine. Bring mixture to a boil then reduce to low and simmer until green beans are tender, about 30 minutes. Serve warm with a sprinkle of fresh parsley or dill if you wish.