What is a Certified Green Restaurant?
Nature.org also has some useful tips to follow when deciding on which restaurants are 'green':
Green Guidelines

• Sustainable seafood – Uses ocean-friendly seafood that comes from a sustainable source (not depleting fish populations)
• Free-range and grass-fed meat – Uses meat that is grass-fed, free-range, raised without antibiotics, organic and/or sustainably raised
• Organic – Uses organic produce or other organic food
• Local and seasonal – Uses regionally (within 300 miles) or locally (within 100 miles) grown produce
• Water – Serves tap water rather than bottled water

More valuable tips from dinegreen.com:
7 Ways to Green Your Dining Experience

1. Choose to dine green by patronizing Certified Green Restaurants®
2. Walk, take public transit, dine at a restaurant close to your home or office, or carpool when dining out
3. Carry pocket-size guides to sustainable seafood, like the ones from Blue Ocean Institute, to help you make smart seafood choices at the fish counter, or your local sushi joint.
4. Bring your own mug for coffee. Make sure to remind staff to make your drink in the cup you bring, not to waste by making it in a to-go cup, then pouring it into your travel mug
5. Consider menu items lower on the food chain. For example, chicken has a lower environmental impact than beef, while sustainable seafood has a lower impact than chicken, and vegetarian and vegan items have the lowest of them all.
6. Bring your own re-usable container and offer it to your server when you ask to take your leftovers home
7. Our research has found that several restaurants claim that 25% of food ordered by customers is wasted and thrown out. Be conscious about what you order and really think about how hungry you are.

For US readers, you can find a green restaurant nearby (covers major metro locations, not all) at http://dinegreen.com/customers/default.asp