Add broth with dissolved cornstarch and bring to a boil; add reserved 1/4 cup pasta water, prosciutto, peas, and tomato, and cook for about 30 seconds. Stir in lemon juice, remove from heat, and let stand another 30 seconds. Fold in cooked pasta and arugula or basil. Salt and pepper to taste, divide between two dinner plates or pasta bowls, and top with shredded Parmesan.