Preheat your oven to 425°F (220°C). Line a large, rimmed baking sheet with parchment paper. Spread the brussels sprouts, carrots, broccoli florets, leeks, minced garlic, and chopped parsley in an even layer across the baking sheet to ensure even roasting.

Drizzle the olive oil evenly over the vegetables, then squeeze the lemon juice across the tops. Sprinkle with salt and freshly ground pepper. Toss everything together right on the pan to evenly coat all the veggies. I like to massage the veggies a bit with my hands at this stage to make sure every piece is well-seasoned.

Place the baking sheet in the preheated oven and roast for 25-35 minutes, stirring the vegetables once about halfway through to ensure even cooking. After 25 minutes, check the veggies; continue roasting until they are golden and crispy to your liking.