1. Bring a pot of water to a boil; add salt generously (or to taste). Add casarecce and cook per package label instructions, tasting a couple of minutes early. Before draining, remove a cup of cooking water.
2. In a heavy-base pan that has a lid, cook scallions and oil over medium heat, stirring, for 1 minute.
3. Add zucchini and cook, stirring occasionally, for 5 minutes.
4. Add wine or vermouth, letting it bubble up. Add 2 Tbsp. parsley. Season with salt to taste, lower heat, cover with lid and cook until zucchini is gorgeously tender, about 5 minutes longer.
5. Tip drained pasta back into its pot. Add zucchini, 3 Tbsp. grated Parmesan and 1/4 cup cooking liquid. Combine thoroughly and taste, adding pepper and more cheese, salt, or cooking liquid, if wished. Stir in butter and most of remaining parsley. Divide between 2 warmed bowls, sprinkle with rest of parsley and more Parmesan, if wished, on serving.