Preheat oven to 180 °C.
Boil potatoes in water with the salt, until cooked.
Peel and mash 2 of the potatoes. Chop 1 tomato and mix with the mashed potato. Add onion, garlic, celery, baby marrows, tuna, mayonnaise and milk.
Season with parsley, paprika, Worcester sauce, lemon juice and pepper.
Spoon into an oven dish and layer the spinach on top.
6. Slice the rest of the potatoes and tomatoes in thin slices and pack on top.
Sprinkle with cheese and bake for 30 minutes or until the veggies are golden on top.
Serve with a salad of your choice.
Use 300 g left-over white fish or chicken instead of the tuna.