Preheat the oven to 425°F. Line a baking sheet with parchment paper.

Spread 1 ½ pounds broccoli and cauliflower florets on the prepared sheet. Drizzle with 3 tablespoons olive oil, add 2 garlic cloves (thinly sliced) and ½ teaspoon crushed red pepper flakes, and sprinkle a couple pinches of kosher salt. Toss the florets on the sheet so everything is evenly coated.

Roast in the preheated oven for 20–25 minutes, tossing once or twice during cooking, until the florets are tender and golden.

Transfer the roasted broccoli and cauliflower to a large bowl. Add ¾ teaspoon lemon zest, 2 teaspoons lemon juice, and 3 tablespoons grated Parmesan. Toss gently to combine.

Taste and season with additional kosher salt and more lemon juice if desired.

Finish with a sprinkling of chopped Italian parsley and serve.