A lapped application zipper has one line of fabric showing on the outside with the appearance that all of the fabric is on one side. It is most commonly seen in slacks and skirts.
A centered zipper application is the easiest but a lapped zipper is not difficult is you take things one step at a time.
Tip If you tend to not have enough seam allowance when you insert lap application zippers, cut your fabric with extra seam allowance, marking and sewing the intended seam line. Trim away excess seam allowance when you are finished.