Preheat oven to 400F.
In a large bowl, toss cauliflower florets with 2 Tbsp olive oil and the salt. Transfer to a baking sheet lined with parchment paper and roast for 20 minutes, stirring after 10minutes.
Stir cauliflower and top with prosciutto pieces. Continue cooking for 10 minutes, or until cauliflower is browned and tender-crisp.
In a small bowl, combine 1 Tbsp olive oil, vinegar, and mustard.
In a large mixing bowl, toss together arugula, hot cauliflower and prosciutto, and vinegar mixture. Season to taste with additional salt and freshly ground black pepper.
To serve, arrange salad on a platter and top with parmesan and cranberries.