Wash and scrub potatoes, chop vegetables, dice onion, mince garlic. Pat everything dry.
Toss potatoes, vegetables, onion, and garlic with olive oil, herbs, salt, and pepper in a large bowl.
Preheat oven to 425°F (220°C). Spread mixture on baking sheet in a single layer.
Roast 25–30 minutes, stirring halfway. Broil 2–3 minutes for extra crispiness if desired.
Rest 2–3 minutes, adjust seasoning, garnish with parsley, and add lemon juice or Parmesan if using.