Frozen vegetables are just as nutritious as fresh vegetables—they're usually frozen at the peak of freshness. The key to not losing nutrients when cooking frozen veggies is to cook them quickly. If you roast them correctly, you'd never be able to tell they didn't come straight from the farmers market. Here's the best technique.
Preheat the oven to 350 degrees Fahrenheit. Lightly coat a roasting pan with cooking spray.
Thaw frozen vegetables halfway so you can separate and spread them out on the pan.
Put the vegetables on the greased roasting pan, and sprinkle them lightly with salt, pepper, rosemary and garlic.
Cover the roasting pan loosely with aluminum foil and put it in the oven.
Let the vegetables cook for 20 minutes.
Remove the roasting pan from the oven, peel back the aluminum foil and turn over the vegetables with a spatula.
Loosely cover the pan again with the aluminum foil and place it back in the oven for 15 minutes.
Remove the the aluminum foil and continue to cook uncovered in the oven for an additional 10 minutes.
Remove the vegetables from the oven. They're ready if you can easily pierce them with a fork. If not, continue to cook them, checking every 2 to 3 minutes until done.