In a large bowl, whisk together eggs, butter, milk and yogurt until smooth. Add in dry pancake mix and stir until a thick batter forms. Place graham crackers in a plastic bag and crush using a rolling pin. Measure one cup of crushed graham crackers and fold into batter.
Preheat a four square waffle iron to manufacturers instructions. Spray with non-stick spray. Spoon about 1/4 cup of batter into each square. Close lid and bake until golden. Lift lid and place half of one chocolate bar on each front waffle. Place 4-5 marshmallows on top of the chocolate, then use a spatula to place the remaining waffles on top of the ingredients.
Gently press the lid of the waffle iron onto the waffles and cook one minute more to melt the chocolate and marshmallows. Remove from waffle iron and cut each sandwich in half.