Preheat the oven to 375F.
Trim the ends of the zucchini & squash and cut them into 3/4" slices.
Core the peppers and cut into 1 1/2" strips.
Trim off the fennel stalks and cut the bulb (through the core) into 1" wedges.
Peel the onion & slice into 1/4" rounds.
Spread the cut-up vegetables on two sheet pans or cookie sheets, spray with olive oil, sprinkle with salt & pepper, and add the thyme sprigs.
Roast for 15 minutes, turn each piece over, sprinkle again with salt & pepper, and roast for an additional 5 - 10 minutes.
Serve hot or at room temperature.