Sage Egg-White Frittata

*Adapted from Martha Stewart's recipe

Ingredients:
1 cup mushrooms, cleaned and sliced
9  large egg whites
3  large eggs
Coarse salt and freshly ground pepper
1/2 teaspoon finely chopped fresh sage, plus 1 tablespoon small whole sage leaves
Extra-virgin olive-oil spray
2 cups mixed greens, trimmed, washed, and dried
Red-wine vinegar and extra-virgin olive oil, for serving

Instructions:
1.  Preheat oven to 375°. Heat a nonstick ovenproof 10-inch skillet sprayed with olive-oil spray over medium heat. Add mushrooms, season with salt and pepper, and cook over medium heat until just barely browned, about 5 - 7 minutes.
2.  In a large bowl, whisk egg whites until they form soft peaks. In another large bowl, whisk whole eggs until foamy and lemon-colored. Fold the egg whites into the eggs.
3.  Sprinkle mushrooms with chopped sage. Pour egg mixture into pan with mushrooms. Distribute whole sage leaves evenly over eggs. Cook until edges are set, about 5 minutes. Transfer to oven, and cook until set and golden brown, about 7 minutes. Drizzle greens with red-wine vinegar and extra-virgin olive oil. Season with salt and pepper. Cut frittata into wedges, and serve over greens.