Rinse the trout and dry them inside and out. Squeeze half of the lemons, stir the juice with salt and pepper. Fold in the oil. Rub the outside and inside of the trout with the marinade.
Peel the garlic cloves and cut them into sticks. Cut remaining lemon in half lengthwise, cut each half into quarters. Rinse the parsley, shake it dry and fill the belly cavities of the fish with the garlic sticks and a piece of lemon each, marinate for about half an hour.
Grill the trout for about 15 min (*), turning a few times to the other side. Serve with the remaining lemon slices and a sauce or butter to taste.
(*) It is advantageous to use special grill baskets for fish, in them the fish turn exceptionally well to the other side during grilling and do not fall apart.