Preheat oven to 425 degrees F. Coat a 3-quart rectangular or oval baking dish with non-stick cooking spray.
Rinse the asparagus in cold water and break off and discard woody bases. In a saucepan cook asparagus in a small amount of boiling water for 3 to 6 minutes or until just crisp-tender. Drain and rinse in cold water again to stop the cooking process. Reserve 4 or 5 spears for later and cut the remaining asparagus into 1-1/2- to 2-inch pieces.
In a large non-stick skillet, cook turkey breakfast sausage, crushing with a spoon to break it up, until no pink remains. Drain off as much of the grease from the pan as possible. Add onion and red bell pepper and continue cooking until vegetables are just tender. Remove from heat and set aside.
Arrange meat mixture in prepared baking dish; top with cooked asparagus, reserving 4 or 5 spears for later.
In a large mixing bowl combine eggs, milk, flour, Parmesan cheese, ground mustard, seasoning salt, and pepper; beat until smooth with a wire whisk. If desired, ingredients can be processed in a blender or food processor instead. Pour egg mixture evenly over sausage in baking dish.
Bake for about 20 to 25 minutes or until a knife inserted near the center comes out clean. Sprinkle with the Swiss cheese and place reserved asparagus spears on top, fanning them out. Bake 3 to 5 minutes more or until the cheese is melted.
Make-Ahead Instructions: Prepare as directed but do not pour egg mixture over the sausage and asparagus, Instead, cover the casserole dish with plastic wrap and keep egg mixture in a separate covered container. Place both in the refrigerator overnight. When you are ready to bake it, remove the casserole and the egg mixture from the refrigerator, whisk the egg mixture and pour it over the sausage and asparagus. Continue as directed.