Smoked Salmon Roll Up

Name: Smoked Salmon Roll-Up
Ingredients: For the Cake; 2 teaspoons poppy seeds; 1/4 teaspoon garlic powder, or more to taste; 1/4 teaspoon onion powder, or more to taste; 1/2 cup (68 grams) all-purpose flour; 1/4 cup (32 grams) cornstarch, plus more for dusting; 6 large eggs, separated, at room temperature; 1/2 teaspoon fine sea salt; Finely grated zest and juice of 1⁄2 lemon; For the Filling & to Finish; 8 ounces (226 grams; generous 1 cup) whipped cream cheese; 4 ounces (113 grams) smoked salmon, finely chopped; 2 scallions, trimmed and thinly sliced; 2 tablespoons finely chopped fresh dill, or to taste; 2 tablespoons snipped fresh chives, or to taste; 2 teaspoons capers, rinsed, patted dry and chopped; Freshly squeezed lemon juice, to taste; Fine sea salt and freshly ground black pepper; Finely sliced cucumber (peeled or not), for finishing (optional); Finely sliced radishes, for finishing (optional); 1 handful arugula, if serving the cukes and radishes as a salad