1 1/4 pounds green beans, trimmed and cut in half
2 tablespoons extra-virgin olive oil
1 onion, chopped
2 portobello mushroom caps, halved and thinly sliced
1/4 cup white wine vinegar
Simmer green beans in salted boiling water 5 minutes. Drain green beans and return skillet to moderate heat. Add oil to the pan. Add onions and saute 2 to 3 minutes. Add mushrooms and season with salt and pepper. Saute mushrooms 3 to 5 minutes with onions, add green beans back to the pan. Heat green beans through and add vinegar. Cook for 1 to 2 minutes. Transfer green beans and mushrooms to a serving plate.