4 cups (1-inch) cubes peeled and seeded butternut squash
5 tablespoons olive oil, divided
Salt and pepper to taste
6 to 8 cups arugula
2 tablespoons lemon juice
1/3 pound sliced prosciutto
1/4 pound ricotta salata, shaved with a vegetable peeler into shards
1/2 cup toasted chopped walnuts
Preheat oven to 375°F.
Toss squash with 3 tablespoons of the oil, salt and pepper and transfer to a large rimmed baking sheet. Roast, tossing occasionally, until golden brown and tender, 30 to 40 minutes; set aside to let cool to room temperature.
Toss arugula in a large bowl with remaining 2 tablespoons oil, lemon juice, salt and pepper, then arrange on plates. Top with squash and prosciutto and garnish with ricotta salata and walnuts. Serve immediately.