Asparagus Frittata II

1. Heat olive oil into a 10-inch oven-proof frying pan over medium high heat. 2. Add onions and salt and cook, stirring occasionally, until onions are softened, about 3 minutes. 3. Add asparagus, reduce heat to medium-low, and cook, covered, until the asparagus are barely tender, 6 to 8 minutes. 4. Pour in eggs and cook until almost set, but still runny on top, about 2 minutes. While cooking, pre-heat oven broiler. 5. Sprinkle cheese (Swiss, Guyere or Mozzarella) over eggs and put in oven to broil until cheese is melted and browned, about 3 to 4 minutes. 6. Remove from oven with oven mitts and slide frittata onto a serving plate. Cut into wedges.