Slice the boneless beef shank into 4-5 inch pieces and place them into a pot of boiling water. Allow to boil for about 5 minutes, then drain and rinse under cold water.

In a large pot, combine rinsed beef, 4 cups of water, sliced ginger, rock sugar, and cassia cinnamon. Bring to a boil, then lower and simmer for about 1 hour.

Once tender, remove and cool at room temperature for about 30 minutes. Wrap tightly in plastic wrap and refrigerate for at least 2 hours or overnight.

While beef chills, heat a non-stick skillet and add oil. Cook scallion pancakes according to instructions, frying until golden and crispy, about 2-3 minutes per side.

Retrieve chilled beef and slice thinly against the grain. Prepare fresh toppings by slicing cucumbers and chopping scallions and cilantro.

Spread hoisin sauce over cooked scallion pancakes. Layer sliced beef, cucumber, scallions, and cilantro on top.

Roll pancakes tightly to enclose fillings. Slice each roll diagonally.

Serve rolls on a platter with additional hoisin sauce for dipping.