Preparation Cook bell pepper in oil and 1 tablespoon butter in a wide 4-quart heavy pot over moderately low heat, stirring occasionally, until softened, 4 to 6 minutes. Add garlic and cook, stirring, 1 minute. Add zucchini, water, salt, and pepper and bring to a boil over moderately high heat, then cook at a brisk simmer, covered, 6 minutes. Remove lid and simmer until most of liquid is evaporated and zucchini is soft, about 6 minutes. Coarsely mash zucchini with a potato masher and add scallion greens and remaining tablespoon butter, stirring, until butter is incorporated.
Preparation Cook bell pepper in oil and 1 tablespoon butter in a wide 4-quart heavy pot over moderately low heat, stirring occasionally, until softened, 4 to 6 minutes. Add garlic and cook, stirring, 1 minute. Add zucchini, water, salt, and pepper and bring to a boil over moderately high heat, then cook at a brisk simmer, covered, 6 minutes. Remove lid and simmer until most of liquid is evaporated and zucchini is soft, about 6 minutes. Coarsely mash zucchini with a potato masher and add scallion greens and remaining tablespoon butter, stirring, until butter is incorporated.