Green Beans and Onions

Ingredients
For the tzatziki:
- Salt, to taste
- 1 cup peeled, seeded and finely   chopped cucumber
- 1 cup plain yogurt
- 2 tsp. minced garlic
For the green beans:
- 2 lb. green beans, trimmed
- 1 large white onion, chopped
- 3 large tomatoes, chopped
- 4 tsp. minced fresh oregano or 2 tsp. dried
- Salt and freshly ground pepper, to taste
- 1⁄4 cup extra-virgin olive oil
Directions
To make the tzatziki, lightly salt the cucumber and drain in a colander for 30 minutes. In a medium bowl, mix together the drained cucumber, yogurt and garlic. Cover and refrigerate until ready to use.Preheat an oven to 425ºF.
To prepare the green beans, bring a large saucepan three-fourths full of water to a boil over high heat. Add a pinch of salt and the green beans. Cook the beans until they turn bright green and are just tender, 1 to 2 minutes. The timing will depend on the age and size of the beans. Drain the beans and plunge them into a bowl of ice-cold water to stop the cooking. Drain and set aside.
Combine the onion and tomatoes in a heavy large baking dish. Add the green beans and oregano, and season with salt and pepper. Drizzle the olive oil over the vegetables and toss to coat. Cover with aluminum foil and roast until the beans are tender-crisp, about 20 minutes. Uncover the dish and continue roasting until just tender, 15 to 20 minutes more (for a total roasting time of 35 to 40 minutes). Stir the beans 3 or 4 times during roasting. Taste and adjust the seasonings with salt and pepper. Transfer the bean mixture to a serving bowl or platter and serve hot or at room temperature, with the tzatziki spooned over the top.