In a mixing bowl, combine flaked mackerel, breadcrumbs, chopped onion, red bell pepper, minced garlic, parsley, beaten eggs, Dijon mustard, salt, and pepper.
Mix the ingredients thoroughly until well combined.
Form the mixture into patties of your desired size.
Heat up vegetable oil in a frying pan on medium heat.
Cook the patties for 3-4 minutes on each side, or until golden brown and cooked through.
If baking, preheat the oven to 375°F (190°C) and bake the patties on a greased baking sheet for 15-20 minutes, flipping halfway through.