Bring a large pot of well-salted water to a boil over medium heat. Set a bowl of salted ice water on the counter. Blanch the fava beans in the boiling water and plunge immediately into the salted ice water. Remove the tough outer casing from the fava bean.
Combine the fava beans in a large bowl with the onions, escarole, and the pecorino (reserve a couple shavings for garnish). Add some red wine vinegar, some olive oil and salt, to taste. Toss to coat the salad with the dressing.
Arrange the salad on serving plates and top with the reserved shaved cheese.