Wash the fish and cut diagonally into thin slices. Heat oil in a coated pan. Carefully fry the fish for 1-2 minutes on each side. Season with salt and pepper. Remove the fish.
Wash the sugar snap peas, cover them with a little water and steam them in a pot for 5-6 minutes until firm to the bite. Prepare rice in boiling salted water according to package instructions. Melt the fat in a small saucepan. Add flour and sweat for 1-2 minutes.
Stir in milk, add stock and simmer for about 1 minute while stirring. Stir in cream cheese. Season sauce with salt, pepper and mustard. Wash the dill, dab dry, pluck flags from the stems and put something aside for garnishing.
Finely chop the remaining flags and stir into the sauce. Drain the sugar snap peas and chill in cold water. Drain rice and rinse with cold water. Layer rice, salmon and mangetouts in 2 greased casseroles, pour sauce over them and bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 10-15 minutes until golden brown.
Garnish with remaining dill and lemon wedges.