Fry pork and onions in oil until fully cooked. Add remaining filling ingredients, and fry until cabbage is wilted and carrots slightly soften. Add shrimp at this time if desired, and cook another few minutes until no longer pink. Set filling aside to cool completely.
Dip one rice paper wrapper into pan of boiling water to soften.
Spoon 2-3 tablespoons cooked filling onto a softened wrap.
Roll one side of wrap over filling, tuck in top and bottom ends, and continue rolling. Place seam side down on counter. Continue filling and rolling wraps until all wraps are rolled.
Eat spring roll as is, or for a crispy wrap, fry in oil.
o fry: let rolls rest 20 minutes before frying, making sure rolls are patted dry of excess water before putting in hot oil.
Fry in 1 inch of hot oil, about 1 1/2 to 2 minutes on each side, then set aside to drain. Drain on paper towels to absorb excess oil.