Preheat the oven to 425°F. Line a rimmed sheet pan with high-heat-resistant parchment paper.
Arrange the peppers, onions, cauliflower, broccoli, and Brussels sprouts in a single layer on the prepared baking sheet.
2 red bell peppers, 1 red onion, 4 cups cauliflower florets, 4 cups broccoli florets, 4 cups Brussels sprouts
Spray the vegetables generously with olive oil and sprinkle them with kosher salt, black pepper, garlic powder, and dried thyme.
Olive oil spray, 1 teaspoon Diamond Crystal kosher salt, ¼ teaspoon black pepper, ½ teaspoon garlic powder, ½ teaspoon dried thyme
Roast the vegetables until fork tender and lightly browned, about 30 minutes. Serve immediately.
Video
Notes
Seasonings, especially salt, are guidelines. Adjust to taste.
Make sure the veggies are thoroughly dry before you coat them with olive oil, and coat them generously.
Roast the vegetables until they are quite brown. If you pull them out of the oven too soon, they won't be properly caramelized.
There's no need to stir the veggies midway through baking. Leaving them undisturbed promotes browning and caramelizing, resulting in superior results than if you had stirred them.
You can keep the leftovers in an airtight container in the fridge for 3-4 days. They are excellent when reheated in the microwave at 50% power. They are also delicious when served cold, antipasti-style.