Preheat oven to 425 degrees F (220 degrees C). Line a baking sheet with parchment paper or aluminum foil.
Discard skin, bones, and any crust from trout and flake fish with a fork. Combine flaked fish with soft bread crumbs, onion, mayonnaise, sour cream, lemon juice, Worcestershire sauce, salt, garlic powder, and black pepper in a bowl. Form mixture into balls and roll each ball in the panko. Arrange balls on the prepared baking sheet.
Bake in the preheated oven until croquettes are lightly browned and crispy, 15 to 20 minutes.
I like to use the food processor to chop onion while processing bread for the soft bread crumbs. If I have more than one cup of the soft crumb mixture, I simply add the remaining to the dry panko crumbs at the end so long as it is not exceed the dry crumbs by half. Easy to adjust to your own taste by adding cheese or herbs.
Per Serving: 278 calories;21.6 g fat;
14.1 g carbohydrates;
10.1 g protein;
36 mg cholesterol;
310 mg sodium.