How to Make It
Preheat oven to 400°F. Toss together bagel pieces and melted butter on a baking sheet; spread in an even layer. Bake in preheated oven until toasted, 8 to 10 minutes, turning once halfway through bake time. Let cool about 10 minutes.
Whisk together cream cheese, water, dill, vinegar, capers, and pepper in a large bowl until well combined (mixture will be slightly chunky). Add spinach, onion, and toasted bagel pieces; toss to coat.
Divide spinach mixture evenly among 4 plates. Top evenly with salmon; sprinkle with bagel seasoning, and garnish with dill sprigs.