Preheat broiler. Arrange bread in 1 layer on a baking sheet, then brush tops with 2 tablespoons oil and season with salt and pepper. Broil until golden brown and transfer to a rack. Cut artichokes lengthwise into 1/4-inch-thick slices and cut prosciutto into matchsticks. Cook artichokes and prosciutto in 3 tablespoons oil in a 10-inch heavy skillet over moderately high heat, stirring, until artichokes are golden, about 4 minutes. Add onion and cook, stirring, until softened. Add peas and cook, stirring, until tender, about 2 minutes. Stir in scallions, mint, and salt and pepper to taste. Spoon mixture over toasts. Drizzle with remaining tablespoon oil and top with parmesan.