Peel and dice the onion and garlic. Remove the beans from the pods (or let them thaw).
Heat 1 tbsp oil in a saucepan and fry the onions and garlic over a medium heat until translucent.
Add the beans tp the pan and cook for 3-4 minutes. Season with salt, pepper and a few splashes of lemon juice. Set the beans aside.
Finely grate the Parmesan. Beat 2 eggs with the cheese and season with some pepper.
Cut the fish fillet diagonally into thin strips.
Season the fish strips with salt and pepper and turn them in the flour to coat; shake off the excess. Heat the remaining oil in a pan.
Turn the fish in the egg mixture to coat.
Place the fish slices in the pan and fry for 3 minutes over a low-medium heat until crispy on both sides. Wash the basil, shake dry and pick off the leaves. Reserve a few leaves and finely chop the remainder.
Whisk the white wine, remaining egg and chopped basil in a heatproof bowl set over a pan of hot water for 5 minutes until creamy. Arrange the beans and fish strips on plates and add the basil sauce. Garnish with basil leaves.