Preheat the oven to 400°F (200°C).
Start by washing the broccoli and cauliflower.
Chop the broccoli and cauliflower into bite-sized florets.
In a large mixing bowl, combine the olive oil, minced garlic, salt, black pepper, and red pepper flakes.
Toss the broccoli and cauliflower florets in this mixture ensuring they're well coated.
Spread out the florets on a baking sheet in a single layer.
Roast in the preheated oven for about 25 minutes, or until the edges are slightly browned.
While roasting, zest and juice the lemon.
Once out of the oven, sprinkle the broccoli and cauliflower with lemon zest and drizzle the lemon juice over them.
Garnish with freshly chopped parsley.