Heat oven to 200C/180C fan/gas 6. In a bowl, mix the beans, zest and juice of half the lemon, the garlic and parsley. Stir through 1 tbsp olive oil and season to taste. Very lightly crush the beans with the back of a wooden spoon, keeping some of them whole.
Cut a large square of baking parchment, spoon the beans onto the centre and top with the fish. Scatter the artichokes around the fish, drizzle over the remaining olive oil, squeeze a little lemon juice over and season well. Bring both sides of the parchment upwards and fold together to create a tight seal, then twist the ends tightly (like a giant sweet).
Put the fish on a baking tray and bake in the oven for 13-15 mins or until the fish is just cooked.