Frittata with Asparagus

6 large eggs, lightly beaten
1/2 cup Parmesan or Gruyere cheese, shredded
8 ounces fresh asparagus, cut into 1/2" pieces
1/4 teaspoon salt
1/4 teaspoon pepper
1 tablespoon olive oil
1/2 onion, chopped fine (optional)
2 tablespoons fresh parsley, basil, or dill

Heat oven to 350 degrees. Use a 10" cast iron skillet or an oven-proof nonstick skillet. Whisk together eggs, cheese salt and pepper. Heat skillet over medium heat. Add onion and asparagus and cook until softened. Add egg mixture. Stir gently until eggs begin to set. Pull cooked eggs back from one edge of skillet allowing any uncooked egg to run to edge of skillet (as in an omelet). When eggs on top are mostly set, place skillet in oven for about 3 minutes until cooked. Run a spatula around the skillet edge to loosen frittata and invert onto warmed serving plate. Serves 4 for breakfast or light lunch.