To a mixing bowl, fold together the hard boiled eggs, smoked salmon flakes, sour cream, mayonnaise, chives, and lemon juice until everything is well combined. Season generously with freshly cracked black pepper. Note: I did not season with salt, as my smoked salmon was plenty salty to season the egg salad. Check for seasoning and add salt if needed, to taste. Cover and chill until ready to assemble sandwiches.
To assemble, place a scoop of smoked salmon egg salad onto a toasted bagel. Top with red onion and avocado slices. Place the top of the bagel on top to form a sandwich. Serve with lemon wedges.