Combine flour and salt in a small bowl; stir well.
Gradually add milk, egg, and margorine, bearing with a wire whisk until smooth.
Cover and refrigerate batter at least 1 hour.
Coat the bottom of a 10-inch nonstick crepe pan or skillet with cooking spray; place pan over medium heat just until hot, nor smoking.
Pour 3 tablespoons batter into hot pan, quickly tilt pan in all directions so that batter covers pan in a thin film.
Cook crepe 2 minutes.
Lift edge of crepe to test for doneness.
Crepe is ready for flipping when it can be shaken loose from the pan.
Flip crepe, and cook 1 minute on other side.
Place crepes on a rowel to cool.
Stack crepes between layers of waxed paper to prevent sticking.
Repeat procedure until all batter is used.
Place one crepe on a serving platter; spread 1/3 cup tuna Salad over crepe.
Top with another crepe, and spread with 1/3, cup Apple Slaw.
Repeat procedure, ending with a crepe, until all crepes, Tuna Salad, and Apple Slaw have been used.
Cover and refrigerate overnight.
Garnish Tuna Stack with a cucumber rose, if desired.
Cur into wedges to serve.