Heat the oil in a deep-fat fryer to 350 degrees F. Cut each egg roll wrapper in half. Brush the edges of each wrapper with beaten egg. Place a prawn at one end of each wrapper, firmly bending it so that it lies straight. Place a mango slice and 2 to 3 sprigs of cilantro beside each prawn. Tightly roll the wrapper around the filling. Deep-fry the egg rolls until they are golden and the prawns are cooked, about 3 to 4 minutes. Drain on paper towels and, if desired, serve with your favourite Asian-style dipping sauce, such as plum or sweet Thai chili sauce.
Note: The egg roll wrappers used to make this dish were 6-1/2" by 6-1/2" in size and made by Frieda'’s Asian Specialties. You will find them in the produce department.