Preheat oven to 450 F. Prepare vegetables. Wash and scrub potatoes. Cut into chunks. Wash and peel carrots. Cut into even strips. Wash cauliflower. Remove leaves, and stem on the bottom so that it sits flat on an even surface. Cut a small yellow onion into large slices.
Prepare the tahini dressing for the cauliflower. Combine, tahini, maple syrup, soy sauce, lemon juice, garlic, and water in a food processor. Blend until smooth and creamy. Remove the dressing, and pour into a small bowl.
Place prepared cauliflower on a baking sheet lined with aluminum foil. Pour the tahini dressing over top. Use a cooking brush to evenly distribute the sauce and cover the cauliflower on all sides. Place on the bottom rack of the oven and bake for 50-60 minutes or until tender.
Prepare the potatoes, carrots, and onion. While the cauliflower is baking combine the prepared potatoes and carrots in a large bowl. Add herbs, salt, pepper, soy sauce, and maple syrup. Toss until combined and evenly distributed.
Transfer the potatoes and carrots to a baking sheet lined with aluminum foil. Add the chopped onion. Evenly spread over baking sheet. If baking sheet is overcrowded use a second baking sheet. Place in the oven, and bake for 30 minutes. Note: The cauliflower is already roasting. Place the potatoes, carrots and onions in the oven after the cauliflower has already been roasting for 20 minutes.
Remove cauliflower and vegetables from the oven. Place cauliflower on the center of a serving tray. Add the potatoes, carrots, and onions all around it. Top with fresh chopped parsley, and garnish with fresh rosemary. Enjoy!