Saute the onions and leek in the oil until transparent. Add the meat, sprinkle with salt and pepper, and cook until done, breaking up lumps.
Add the cumin and the chopped egg whites and mix well.
Cut each spring roll skin into 3 strips of equal width (If the dough is not precisely square, use the slightly larger dimension for the length of the strip.) Lay out 3 to 4 strips on your work surface.
Place a rounded tsp of the meat mixture toward the bottom right hand corner of each strip. Fold that corner diagonally over to the top left-hand corner, forming a triangle. As you fold, be certain that the side of the strip lines up perfectly with the folded portion. Continue as if folding a flag, alternately folding the bottom corners in a diagonal pattern. Seal the final flap with a bit of the flour paste.
Deep-fry in small batches until golden brown (about 3-5 minutes) and drain on paper towels.