How to Make It
Preheat oven to 475°F. Toss together broccoli, cauliflower, Brussels sprouts, carrots, olive oil, salt, and pepper on a large rimmed baking sheet.
Bake in preheated oven 10 minutes, undisturbed. Remove from oven; quickly toss vegetable mixture with walnuts and garlic. Return to oven, and bake until caramelized and tender, 5 to 10 more minutes. Squeeze lemon over veggies just before serving.