Place fish in a small pan, pour over milk, cover and simmer until fish flakes. Strain and reserve milk. Flake fish, discard skin and bone. Melt butter, stir in flour and cook 1 min. Stir in reserved milk, bring to the boil and cook a further min. Stir in fish and half the cheese. Season.
Make pancakes. Cut three circles the size of ramekin dishes from each pancake. Layer the pancake circles, fish sauce and tomato slices in ramekin dishes, finishing with pancake circle. Sprinkle with remaining cheese. Bake 375 F. approx. 15 mins. until cheese is brown. Garnish with lemon and tomato slices.