Give your leftover beans and sprouts a second chance in this tasty egg dish.
Preheat the broiler. Put 1 tablespoon of the olive oil in a medium nonstick skillet and turn the heat to medium. Add the onions and cook until just softened, about 5 minutes. Add the string beans and sprouts and continue to cook until the beans and sprouts are warmed through, about 3 more minutes.
Meanwhile, beat the eggs and cheese together and season with salt and pepper. Pour the eggs over the vegetables and shake gently to distribute everything evenly. Cook the frittata, tilting the pan occasionally to redistribute the uncooked eggs towards the sides of the pan, until the eggs are set, about 10 minutes.
When the eggs are set, run the pan under the broiler for a minute or two until the top is just golden and bubbling. Cut into wedges and serve.