Heat oven to 350°F. Grease a 9x13-inch baking dish. Brown onion and bacon in a skillet over medium-high heat; drain and spread in dish. Sprinkle with 1 1/2 cups cheese. Arrange asparagus over cheese.

Whisk together eggs, flour, mustard and pepper in a bowl; add milk and pour evenly over asparagus.

Bake 30 to 35 minutes or until center is set and edges are brown; top with remaining 1/2 cup cheese and parsley.