In a food processor or blender, purée the fava beans with the cheese and 2 tablespoons of water until smooth and spreadable (add a little more water to thin, if necessary). Season to taste with pepper.

On a lightly floured surface, arrange the pastry sheet with a long side facing you and brush the edge of the far side with beaten egg. Spread the fava mixture evenly on top of pastry, avoiding the egg-brushed edge. Starting with the side nearest you, roll the pastry in a jelly-roll fashion into a log and wrap in plastic. Chill pastry log, seam side down, until firm, at least 1 hour, and up to 2 days.

Preheat the oven to 400°. Lightly grease a large baking sheet with oil or line with parchment paper. Cut log crosswise into 12 (¾-inch) pinwheels and arrange, cut sides down, 1 inch apart on baking sheets. Bake pinwheels in batches, rotating halfway through, until golden, 18 to 20 minutes. Transfer pinwheels to a wire rack and cool.

Pass the boiled eggs through a sieve or finely grate; season to taste with salt and pepper. Toss the mesclun with oil and lemon juice, and season with salt; divide among plates. Top with the pinwheels and egg crumbles.