Green Beans with Tomatoes

1 T. olive oil
1 medium onion, halved and thinly sliced
1/2 tsp. dried oregano
1 can (14.5 oz.) whole peeled tomatoes in puree
1 lb. green beans, trimmed
Coarse salt and ground pepper

In a large skillet with a tight-fitting lid, heat oil over medium-high. Add onion and oregano, and cook, stirring frequently, until lightly browned 2 to 3 minutes. To skillet, add tomatoes and their puree, breaking up tomatoes with a spoon or your fingers. Stir to combine. Add green beans, 1 1/2 tsp. salt, and 1/2 tsp. pepper and bring to a boil. Reduce heat to medium-low; cover and simmer, stirring occasionally, until green beans are soft, about 30 minutes. Serve.