Clean and wash the fish. Peel the potatoes and cut them into long strips. Cut the onions, peppers and tomatoes into slices. Cut the peeled garlic into slices.
Sprinkle the inside and outside of each trout with salt, black pepper and cumin. Stick chopped garlic cloves and a bunch of dill (with stems) in the belly of each fish. Pour lemon juice and olive oil inside and out and leave to season for 20 min.
Transfer the trouts to the baking bag, tie it and poke 2-3 holes in it with a toothpick on the top side.
Transfer the baking bag to the tray and bake in a preheated 356°F (180 °C) oven on the middle rack about 35 min. with the fan on.
Transfer the ready dish from the bag to a suitable serving plate and garnish with lemon slices and a sprig of dill.