Heat broiler, with rack in top position. Divide gnocchi among four 8-ounce shallow baking dishes or place in an 8-inch square baking dish. Season with salt and pepper,then top with dollops of marinara sauce and ricotta cheese. Sprinkle with grated Parmesan and broil until tops are browned in spots and gnocchi are heated through, 3 to 5 minutes, rotating once.