Preheat broiler to low.
In a large mixing bowl, whisk together eggs and milk until well combined.
Stir in Parmesan cheese, parsley and salt and pepper and set aside.
In a large, ovenproof skillet, cook bacon over medium heat until slightly crisp.
Remove bacon with a slotted spoon and reserve on a plate.
Add onions to remaining bacon grease in pan and cook over medium heat until soft, about 5 minutes.
Add asparagus and cook 2 to 3 minutes until crisp-tender.
Return bacon to pan and toss gently to combine. Then distribute bacon and asparagus evenly over the pan.
Gently pour egg mixture over bacon and asparagus and cook over medium heat until edges begin to set.
Remove pan from heat and place in preheated broiler. Cook 3 to 4 minutes, until top is set and puffy and just beginning to brown.
Remove pan from an oven and slide a spatula around the edges of the frittata to loosen.
Slide onto a large serving plate, cut into wedges and serve immediately.