Preheat your oven to 425°F. Line a baking sheet with parchment paper for easy cleanup.
In a large bowl, toss the broccoli and cauliflower with olive oil, minced garlic, salt, and black pepper until evenly coated.
Spread the well-coated vegetables in a single layer on the baking sheet, making sure they have room to roast evenly.
Roast in the preheated oven for about 25 minutes until tender and lightly charred along the edges. If you like, drizzle with the lemon juice before serving. Garnish with optional Parmesan cheese. Enjoy this healthy side dish!