Salmon that is cured before it is smoked at low temperatures results in a firm, sliceable fish called lox. Salmon smoked at higher temperatures flakes easily. Both types of smoked salmon work in this strata.
Lightly grease a 3-quart rectangular baking dish. Arrange half of the bagel pieces in the prepared baking dish. Top with cream cheese, salmon, onion, and chives. Arrange the remaining bagel pieces over salmon mixture.
In a medium bowl combine eggs, milk, cottage cheese, dill, and pepper. Pour evenly over ingredients in dish. Press lightly with a rubber spatula or the back of a large spoon to moisten all of the bagels. Cover with plastic wrap and chill for 4 to 24 hours.
Preheat oven to 350 degrees F. Bake, uncovered, for 45 to 50 minutes or until a knife inserted near the center comes out clean and the edges are puffed and golden. Let stand for 10 minutes before serving.