Preheat oven to 425ºF. Line 2 rimmed baking sheets with parchment paper for easy cleanup.
In a small bowl or measuring cup, combine the chicken stock, olive oil, salt, black pepper + dried sage. Stir to combine.
1/2 cup chicken stock, 1/4 cup olive oil, 2 teaspoons salt, 1 teaspoon pepper, 1 teaspoon dried sage
In a large bowl, combine the cauliflower, celery, carrots, mushrooms, leek, onion, pecans, fresh rosemary, and fresh thyme. Pour over the chicken stock mixture. Stir well to combine.
1 head cauliflower, 4 ribs of celery, 2 medium carrots, 12 ounces mushrooms, 1 leek, 1/2 yellow onion, 1 cup raw pecans, 1 tablespoon fresh or dried thyme, 1 tablespoon fresh or dried rosemary
Spread in an even layer over 2 baking sheets. You don't want to overcrowd the stuffing, otherwise the vegetables won't caramelize.
Roast in the oven for 40-45 minutes, until golden brown. No need to flip the vegetables while roasting.
Remove from the oven. Serve warm.
Leftovers will keep refrigerated in an airtight container for at least 5 days. Or frozen for up 6 months.