Step 1
Preheat the oven to 425 degrees F (220 degrees C). Line 2 baking sheets with heavy-duty aluminum foil.
Step 2
Combine broccoli and cauliflower florets with 2 tablespoons olive oil in a large mixing bowl. Add 1 teaspoon rosemary and 1 teaspoon thyme. Season with salt and pepper. Spread mixture onto 1 of the prepared baking sheets.
Step 3
Add Brussels sprouts to the same large mixing bowl. Add 3 tablespoons olive oil and season with salt and pepper. Spread mixture onto remaining prepared baking sheet.
Step 4
Roast in the preheated oven gently stirring every 5 minutes until broccoli and cauliflower are lightly browned and Brussels sprouts are dark brown 20 to 30 minutes.
Step 5
Meanwhile place sweet potatoes into the mixing bowl. Add 3 tablespoons olive oil remaining rosemary and remaining thyme. Season with salt and pepper and stir to combine. Remove roasted vegetables from the oven and transfer to a large disposable foil pan. Place sweet potatoes onto 1 of the foil-lined baking sheets used prior.
Step 6
Roast potatoes in the hot oven until tender stirring every 5 minutes for 30 to 35 minutes. Remove roasted sweet potatoes and transfer to the disposable foil pan.
Step 7
Add yellow bell peppers and red bell peppers to the same large mixing bowl. Separate red onion quarters into pieces and add to the bowl. Stir well to coat vegetables in oil remaining in the bowl. Transfer mixture to the other foil-lined baking sheet.
Step 8
Roast peppers in the hot oven stirring every 5 minutes for 15 to 20 minutes. Transfer to the disposable foil pan with the other cooked vegetables. Stir to mix. Serve immediately or cover with foil to be reheated later.