Preheat oven to 350°F (175°C).
To blanch asparagus, in a large frying pan, bring approximately 3 inches of water to a boil. Stir in 1 tbsp of salt.
Add asparagus, arranging in single layer. Cook at a medium boil until slightly underdone, about 3 minutes depending on thickness.
Drain on paper towel and let cool.
Whisk parsley, water, 1/4 tsp salt and pepper into beaten eggs.
Stir in cheese.
Set aside 6 whole asparagus spears for garnish.
Cut remaining asparagus on the angle, into 1 inch pieces and set aside.
In a heavy (or non-stick) oven-proof 12 inch skillet (with a cover), sauté red pepper in 2 tbsp olive oil until barely tender-crisp, about 5 minutes.
Stir margarine into pan. Add onion and asparagus and sauté for one minute.
Pour egg mixture into pan and stir gently to distribute vegetables, without scraping the bottom of the pan. Bake for 10 minutes, covered, on the middle rack in pre-heated oven. Remove cover and bake until the edges are browned, eggs are set and centre is just firm to the touch. Let rest for 5 minutes.
Using a narrow, flexible spatula, loosen the sides and bottom of the frittata then carefully cover pan (which will still be hot) with a large, warmed serving platter. Protecting your hands with potholders, flip the frying pan over onto the platter.
You may also serve frittata right from the pan.
Cut into 6 wedges and garnish each with reserved asparagus spears, lemon wedges and sprigs of parsley.