In a large skillet, over medium high heat, heat oil to 375 degrees F.
In a medium skillet over medium heat, saute coleslaw, water and onions until tender. Add the chopped corned beef, pepper, and salt and saute 1-2 minutes. Transfer to a large bowl and mix in cooked potatoes.
In a small bowl, combine flour and 2 tablespoons water in a bowl until it forms a paste.
To assemble egg rolls, lay one egg roll wrapper with the corner pointed toward you. Place 1/3 cup of the cabbage mixture on egg roll wrapper and sprinkle with 2 tablespoons of cheese. Fold corner up over the mixture. Fold left and right corners toward the center and continue to roll. Brush a bit of the flour paste on the final corner to help seal the egg roll.
Place egg rolls into heated oil and fry, turning occasionally, until golden brown. Remove from oil and drain on paper towels or rack. Serve with thousand Island dressing.