Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper for easy cleanup.
Prepare vegetables – Peel and cube the butternut squash, trim and halve the Brussels sprouts, and chop the onion.
Season – In a large bowl, toss the squash, Brussels sprouts, onion, and garlic with avocado oil, rosemary, thyme, salt, and pepper until evenly coated.
Roast – Spread vegetables in a single layer on the baking sheet. Roast for 30-40 minutes, stirring halfway through, until golden and tender.
Serve & enjoy – Garnish with extra fresh herbs if desired and serve warm.