1
Adjust racks to top position and preheat oven to 425 degrees. Bring a large pot of salted water to a boil. Wash and dry produce.
Trim and halve zucchini lengthwise; cut crosswise into 1⁄2-inch-thick half-moons. Zest and quarter lemon. Halve, peel, and thinly slice onion.
Toss zucchini on a baking sheet with a drizzle of oil, salt, and pepper. Roast on top rack, tossing halfway through, until tender and lightly browned, 14-16 minutes.