Heat the olive oil in a large skillet over medium heat. Add the onion, celery and salt and cook until soft, 5 to 7 minutes. Add the garlic and caraway and cook for another minute. Add the pastrami and cook until heated. Turn off the heat and stir in the shredded cabbage. Season with soy sauce, apple cider vinegar and black pepper. Taste and adjust as desired.
Mix together the flour and 1 tablespoon water in a small bowl to form a paste (it will act as your glue). To fill an eggroll, orient a wrapper in front of you like a diamond. Spread a horizontal line of filling across the bottom half of the wrapper, then fold the bottom corner up over it. Fold in the outer sides, then roll up the rest of the way, sealing well with the flour paste. Repeat with remaining wrappers and filling.
Heat 1/2-inch canola oil in a heavy bottomed pot to between 360 and 370 degrees F.
Fry eggrolls until the outsides are golden brown, turning once, for a few minutes on each side. Transfer to a paper towel or wire rack, let cool slightly and serve with mustard.