Saute slice scallion in margarine, until soft. Beat egg with water and lemon thyme, add salt and pepper and pour over cooked scallion. Allow to cook until top is set. Lay cheese over !/2 of egg mixture, allow to melt briefly, fold omelet in half and slide onto serving plate. Garnish with a sprig of lemon thyme. Serve with Herb Peasant Bread, toasted.