Chop 8 of the scallops and keep the remaining 16 whole to add near the end of the cooking time.
Heat the butter and oil in a heavy-based pan and cook the onions and garlic until soft. Add the chopped scallops, zucchini and rice. Stir well, then add the wine.
Toast the rice by frying it until it has absorbed all the wine and fat. After a minute or so, begin to add the hot stock, a ladleful at a time, stirring constantly between addition until the stock is absorbed.
Cook for 15–20 minutes, or until the rice is cooked, but each grain is still slightly firm in the centre. Taste and adjust for salt and pepper.
Towards the end of the cooking time, add the whole scallops. Cook for a few minutes, then stir in the fresh herbs and the lemon juice.
Remove from the heat and stir in the butter. Cover for few moments, then serve.