In a skillet coated with cooking spray, cook onion and garlic over medium heat for 3 minutes or until tender. Remove from the skillet. Add spinach to skillet in batches, cooking for 1 minute or until wilted. Remove from the heat.
In a large bowl, beat the eggs/egg substitute until frothy. Stir in the onion mixture, cooked spinach, mozzarella, blue cheese, tomatoes and nuts. Place in a 10-in. ovenproof skillet coated with cooking spray.
Bake, uncovered, at 400° for 30-35 minutes or until a knife inserted near the center comes out clean.