Position a rack in the upper third of the oven and preheat to 425°F.
In a medium bowl, combine the spinach, cream cheese, mayonnaise, scallion, parsley, pickled jalapeño, lemon zest, and pepper. Stir until smooth.
Working over the bowl, break the salmon into flakes; you should have about 2 cups. Stir until combined. Stir less for a chunkier spread or more for a smoother spread. Season lightly with salt if needed.
Transfer the dip to a shallow baking dish and spread evenly.
In a small bowl, combine the panko and butter and season lightly with salt. Sprinkle the panko evenly over the dip and bake until golden and heated through, 6 to 8 minutes.
Serve warm with crackers or baguette slices for scooping.
