Preheat the grill to its hottest setting, with the oven shelf set as close to the element as possible.
Lay the courgettes on your largest baking tray and paint both sides with the oil. Place the courgettes under the grill and cook for 8–10 minutes, until they are charred and softened.
Remove the oven tray, turn the courgettes and return to the grill for a further 8–10 minutes, until nicely charred. (They should be limp and properly blackened in places on both sides, not half-heartedly browned, as they are tastier when beaten up by the grill.) Don’t turn off the grill.
When they are cooked, transfer the courgettes to a bowl and add the beans and basil leaves. Mix in the garlic, lemon juice and a very generous glug of oil. Season to taste with sea salt, if need be.
Slash the fish, only very lightly, three times on each flank. Rub each one all over with olive oil and love. Mix the rosemary with the sea salt and season the fish, taking care to rub the seasoning into the slashes.
Place the seasoned fish under the grill – but not so close that they burn before the flesh is cooked. After 5 minutes, turn the fish over and do the other side – when done, they should be browned and quite crisp.
Serve the fish with the courgettes, beans and basil.