In a large mixing bowl, combine the cooked fish, breadcrumbs, beaten egg, mayonnaise, Dijon mustard, lemon juice, chopped parsley, salt, and pepper. Mix well until all ingredients are combined.
Form the mixture into small patties, about the size of your palm.
Heat a frying pan over medium heat and add a bit of oil. Cook the fish cakes for about 3-4 minutes on each side, or until golden brown and cooked through.
In a large salad bowl, combine the mixed greens, cherry tomatoes, cucumber, and red onion.
In a small bowl, whisk together the olive oil, balsamic vinegar, salt, and pepper. Drizzle over the salad and toss to combine.
Serve the fish cakes on top of the salad. Enjoy!