The simple answer to why roasted vegetables from a restaurant taste so good: lots of fat and salt and high heat. Refer to the list below and watch Ethan Chlebowski's useful instructional video for the full answer.
- Salt is the seasoning, not herbs or spices
 - Use fats, thoughtfully
 - Embrace high heat (+ convection)
 - Give the vegetables space & time
 - Try parboiling
 - Frozen vegetables are your friend
 - Add flavor enhancers after roasting