Roasting vegetables with aromatics, salt, pepper, and olive oil is easy, mostly hands-off, and always produces the best results.
Preheat oven to 450 degrees. Quarter and cut zucchini into 1 1/2-inch chunks. Thinly slice onion.
On a rimmed baking sheet, toss zucchini and onion with oil, thyme, salt, and pepper. Roast 30 minutes, tossing halfway through. Serve.