In a non-stick oven-safe skillet, melt the butter & garlic together over low heat.
Add the onions and cook for 15 minutes. Turn the heat up to medium and cook for an additional 15 to 20 minutes. The onions should cook down completely and caramelize. Season with salt and pepper then set aside to cool.
While the onions cool add the eggs to a large mixing bowl and whisk.
Stir in the asparagus pieces, bread crumbs, asiago cheese, parsley, caramelized onions, salt and pepper.
Pour back into the non-stick skillet (oven-safe) and bake at 350 degrees for 20 minutes or until frittata puffs.