Heat the olive oil in a large skillet or pot over medium heat. Add the chopped onion and sauté until softened and translucent, about 5 minutes.
- Add the minced garlic and sauté for an additional 30 seconds until fragrant.
- Stir in the tomato paste and cook for 1-2 minutes, allowing it to darken slightly.
- Add the diced tomatoes (with their juices), dried oregano, salt, and pepper. Stir to combine.
- Pour in the water or vegetable broth, and bring the mixture to a simmer.
- Add the green beans, stirring them into the tomato sauce. Cover the pot and reduce the heat to low.
- Let the beans cook slowly for 30-40 minutes, stirring occasionally, until the green beans are tender and the sauce has thickened.
- Once the beans are cooked, taste and adjust seasoning if necessary.
- Garnish with fresh parsley and dill (if using) before serving.