Preheat your oven to 425°F (220°C).
In a large mixing bowl, combine the broccoli, cauliflower, carrots, bell peppers, and red onion.
In a small bowl, whisk together the olive oil, minced garlic, oregano, thyme, salt, black pepper, and red pepper flakes if using.
Pour the olive oil mixture over the vegetables and toss until they are evenly coated.
Spread the vegetables in a single layer on a large baking sheet.
Roast in the preheated oven for 25-30 minutes, stirring halfway through, until the vegetables are tender and slightly caramelized.
Remove from the oven and garnish with fresh parsley before serving.