Preheat the grill to medium.
Place the eggs into a bowl, season with salt and freshly ground black pepper and beat well.
Add the salmon, butter beans and rocket and mix well.
Heat the oil in a non-stick frying pan over a medium heat. Pour the egg mixture into the pan and cook for 2-3 minutes, until the base is golden-brown and the frittata is almost set.
Place the frittata under the grill and cook for a few minutes, until golden-brown on top and completely set.
To serve, cut the frittata into wedges and place onto serving plates.