Preheat oven to 350 degrees F (175 degrees C). Grease a baking sheet with cooking spray.
Fill a large pot with water and lemon-lime soda; bring to a boil. Add halibut chunks, a few at a time, and cook until they float to the top, 30 to 45 seconds. Transfer to a colander to drain.
Heat olive oil in a large skillet over medium-low heat. Add onion, zucchini, carrot, celery, and garlic; cook and stir until softened, about 5 minutes. Sprinkle seasoned salt on top.
Flake halibut chunks into a large bowl. Stir in onion mixture, bread crumbs, mayonnaise, egg, parsley, and cayenne pepper.
Scoop halibut mixture onto greased baking sheet with a cookie scoop; flatten into cakes.
Bake halibut cakes in the preheated oven until golden, 10 to 12 minutes.
