Prep Time: 45 minutes
In a small mixing bowl, soak the bread cubes in the milk. Stir to combine and set aside. Mince the fish and place into a large mixing bowl. Add the egg, 1/4 cup bread crumbs and soaked bread cubes. Season with a pinch of salt and pepper and mix until thoroughly combined. Set aside for a few minutes. Meanwhile, whisk together the mayonnaise, garlic, lemon juice and zest along with a pinch of salt and pepper until combined. Refrigerate until ready to use.
In a large sauté pan, heat 1/4 cup oil over a medium flame until hot. Place the remaining breadcrumbs onto a plate and spread out evenly. Season with a pinch of salt. For each cake, form 1/4 cup of the fish mixture into a ball and flatten with the palm of your hand. Coat on both sides with the breadcrumbs, shaking off any excess. Cook in batches, leaving room for the cakes to fry, about 7 minutes on each side, or until the fish is completely opaque when cut in half. Remove any cooked cakes to a plate lined with paper towels. Replenish the oil, if necessary, heating until hot before adding fresh cakes.Line a platter with the arugula and season with a pinch of salt and pepper. Top with the fish cakes, aioli and avocado slices. Season with salt and pepper to taste.