Place the fish in a large, deep frying pan and pour in the milk. Add the bay leaf, bring to a boil, then reduce the heat and simmer gently for about 7 minutes until the fish is just cooked. Strain off the milk and set the fish to one side.
Meanwhile, boil the potatoes in water for 15 minutes until tender, adding the peas for the final 3 minutes of cooking time. Drain well, then add them back into the pan and mash the potatoes and peas with a potato masher. Stir in the lemon zest and parsley.
Fry the bacon over medium-high heat until crisp. Carefully flake the fish into large flakes. Add the fish and bacon to the mash. Leave until cool enough to handle, then form into 4 fish cakes.
Dust each of them in the flour, then coat in egg, and finally cover in breadcrumbs.
Heat the olive oil in a frying pan over medium-low heat, and cook the fishcakes for about 3-4 minutes per side until golden and crisp.
While the fishcakes are cooking, boil the green beans for about 5 minutes, until tender. Drain well.
Serve the fishcakes with the green beans and tartar sauce.