Prepare salmon cakes: In a large bowl, flake salmon with a fork. Add green onions, bell pepper, jalapeño, lemon zest, mustard, egg whites, mayonnaise, and 1 cup panko. Stir with a fork to combine lightly. Form mixture into 8 cakes, each roughly 3 inches in diameter and 1/2-inch thick.
Combine remaining 1/2 cup panko with black pepper on a large plate. Working carefully and with one hand, press both sides of each cake into panko, squeezing the mixture gently so that it does not crumble. Refrigerate at least 30 minutes while preparing herbed yogurt.
For herbed yogurt: Combine all ingredients in a small bowl. Allow to sit at room temperature, covered, 30–45 minutes.
Preheat oven to 375°. Spray a foil-lined baking sheet with nonstick cooking spray.
In a large nonstick skillet, heat 1/2 tablespoon olive oil over medium heat until nearly smoking. Working in batches, brown cakes well on both sides, then remove to prepared baking sheet. Repeat with additional cakes in remaining oil. Transfer cakes to the hot oven for 7–9 minutes, or until heated through. Drizzle with herbed yogurt and serve.