Bring a large pot of water to a boil. Add the fava beans and cook for 30 seconds. Drain the beans and transfer to a bowl of ice water to stop the cooking process.
Combine the fava beans, lemon zest, lemon juice, pine nuts, mint, basil, garlic, salt, and pepper in the bowl of a food processor and blend until finely chopped. With the machine running, slowly add the olive oil and blend until smooth. Transfer the pesto to a small bowl and stir in the cheese.
For the Crostini:
Preheat the oven to 400°F. Place the bread slices on a large rimmed baking sheet and brush with 2 tablespoons of olive oil. Toss the shrimp with the remaining 2 tablespoons of olive oil and arrange on another baking sheet. Season with salt and pepper. Bake for 8 to 10 minutes, until the bread is lightly toasted and the shrimp are cooked through.
Spread some pesto over each piece of bread and arrange the shrimp over the pesto. Top each toast with a few shards of cheese and serve.