Bring a large saucepan of lightly salted water to the boil. Add the broad beans and simmer rapidly for 3 minutes, then add the peas. Bring back to the boil, then drain immediately and tip the broad beans and peas into a bowl of ice-cold water.
Meanwhile, toss the fennel with the lemon juice and season with black pepper.
Arrange the sorrel leaves in a large serving dish, then pile the fennel on the leaves, scatter over the peas and broad beans and sprinkle with shredded mint leaves.
Drizzle over the avocado oil, if using, then season with a little salt and plenty of black pepper. Serve immediately with lemon wedges.