Combine the ricotta, goat's cheese, parmesan, basil and lemon zest in a bowl. Season with salt and pepper.
Gently open the zucchini flowers and spoon a heaped teaspoon of the mixture inside. Close to encase the filling.
Combine the flour and water in a bowl, stirring to make a smooth batter.
Half-fill a large, heavy-based saucepan with oil for deep-frying. Heat the oil to 180°C (350°F) or until a piece of bread browns in 15 seconds.
Dip the flowers in batter and fry in batches, turning occasionally, for 3-4 minutes, until crisp and golden-brown.
Remove using a slotted spoon and drain on paper towel. Season with salt. Serves 4.