Fresh beans are readily available during the late summer months, and they are surprisingly easy to cook with. Simply shell the fava beans and cook them for three minutes in boiling, salted water, then transfer them to a bowl filled with ice water to keep them from overcooking.
Arrange the baguette slices on a baking sheet, drizzle with olive oil, and toast under the broiler until just golden, checking every minute to make sure the bread doesn't burn. Set aside.
Meanwhile, bring a pot of salted water to a boil over high heat. Cook the fava beans for 3 minutes; transfer them immediately to a bowl filled with ice water to stop the cooking process. After they've cooled slightly, add the beans to the bowl of a food processor with the lemon zest and juice, olive oil, cider vinegar, and garlic. Turn the processor on and purée until the mixture is smooth. Add the pepper flakes and salt and pulse until fully combined.
To assemble the crostini, spread the toasts generously with the fava bean mixture, then top with mint leaves and pecorino shavings. Serve immediately.