Cook bacon and onion together in skillet until brown; drain and set aside.

Slice each bagel into 4 thin slices.

Arrange 6 bagel slices in the bottom of a greased 9x13 baking dish.

Cover with the bacon and onion mixture, top with 1 cup Cheddar cheese then remaining bagel slices.

Whisk together eggs, milk, parsley, and pepper. Pour the egg mixture over the bagel layers and top with remaining cheese. Cover and refrigerate 8 hours or overnight.

Preheat oven to 400°. Bake, uncovered, 25-30 minutes, or until eggs are firm. Serve warm.