Get a wood or coal fire going and allow it to burn down until the logs/coals are glowing red, white and ashy around the edges, and have a nice low flame. Rub the interior and exterior of the trout with the olive oil, then rub the interior with the salt and pepper. Cut the lemon in half and cut one of the halves into 1/4-inch thick slices.
Arrange the lemon slices and herb sprigs inside of the trout, it’s alright if they’re sticking out a little. Wrap the outside of the trout in the fig or grape leaves over the stuffing opening. Tie the trout to a stick to hold over the fire, adjusting the distance as necessary to ensure that the fish is cooking but not burning (a little char is ok, but you don't want it to catch on fire).
Roast until the fish is completely cooked through and flakes easily with a fork. Remove from the stick, cut the fish open, and squeeze the remaining lemon half over it. Serve immediately.