Wash the fish fillet, dab dry and cut into 2-3 cm wide strips (approx. 50 g each). Sprinkle with lemon juice and put aside. Peel and wash potatoes and carrots and cut them roughly into pieces.
Cover and cook in boiling salted water for about 20 minutes. Beat the egg with some salt, pepper and about 1/3 of the paprika powder in a deep plate. In a 2nd deep plate, mix breadcrumbs and the rest of the paprika powder.
Line a baking tray with baking paper and brush with oil. Dab fish dry. Turn the strips first in egg, then in breadcrumbs and lay them on the baking tray. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 20 minutes.
Turn over after about 10 minutes. Drain the potatoes and collect the cooking water. Measure 125-150 ml, add to the potatoes and carrots and mash coarsely. Season to taste with salt and pepper if necessary and arrange on plates with the fish fingers.
Garnish with lemon wedges and parsley.