Pre-heat oven to 425 degrees and line a baking sheet with foil. Spray foil with cooking spray and set aside.
In a large resealable plastic bag, add all remaining ingredients (potatoes through pepper) and seal tight. Shake well so that vegetables are evenly coated in oil and salt.
Spread oil coated potatoes, cauliflower and garlic in an even layer on baking sheet and roast until golden brown, about 35-45 minutes, stirring once halfway through.