Preheat oven to 180°C.
Sprinkle trout inside and out with lemon juice, season with salt and pepper. Cut the vegetables into fine strips and slice the lemon. Stuff trout with half of the finely chopped vegetables.
Place two large pieces of parchment paper, one trout on each. Spread remaining vegetables on trout, top each trout with 3 lemon slices each. Fold ends of paper over each other, folding ends to make parcels.
Cook trout in preheated oven for about 25 minutes.
Meanwhile, cook potatoes in steamer over steam for about 20 minutes, peel. Slightly heat rapeseed oil in a pot, toss potatoes and parsley in it, add salt.
Unwrap trout and serve with parsley potatoes and vegetables.