Mix the courgettes, spring onions, mint and flour together in a large bowl, then stir in the eggs. Mix well, season with salt and pepper, then gently fold in the ricotta.
Heat a little oil in a large frying pan. Add 4 separate heaped tablespoonfuls of the batter, flatten slightly and cook for about 3 minutes on each side until golden. Transfer the fritters to a baking sheet and keep warm in a low oven while you repeat with the remaining batter, adding a little more oil to the pan as necessary.
Serve the fritters immediately with a spoonful of lemon-flavoured mayonnaise.