Preheat the grill, setting the burners to medium.
Oil the grate.
In a large bowl, whisk together the eggs, milk, sugar
and vanilla.
Dip each bread slice in the egg mixture and soak for several
seconds. Set aside on a plate.
Grill the bread slices for 1 minute, then rotate them
a quarter-turn and continue to grill for 1 minute. Flip
the bread and top with the marshmallows and cookie pieces.
Close the lid and cook for 1 to 2 minutes, checking regularly,
until the French toast is cooked through and the chocolate
is melted.
Serve topped with banana slices and drizzled
with maple syrup.