Fuse one piece of your lightweight interfacing to your zipped pocket piece and one to the back of the lining where your pocket will be positioned.
To create the zipped pocket lay one interfaced piece right sides together in the centre of lining piece and pin at the edges.
Measure the teeth of your zipper and mark a box with fabric marker or pencil of that length with a height of 1/2” (1cm) in the centre of piece about 1” (2cm) from the top. I use a Frixion pen which disappears when heat is applied.
Draw a triangle at each end within the box and connect with a central line, this is where you will cut through both layers once sewn.
Sew around the outside of the box and then cut through the triangles and central line. Remove your pins.
To ensure your front piece lays flat, I like to do a bit of extra manipulating with my iron. Slide your iron up to the seam between the pieces and repeat for all 4 sides. You should end up with this.
Push the pocket piece through the lining piece to the back.
Press well and manipulate the fabric to lay flat. If you press from the front first, no matter how awkward then any puckers will be on the back.
I like to zig zag the ends of my zip before attempting to sew it into the gap. I used a zig zag stitch of 4.5width and 0 length and just went over the open end. (I also did my closed end because my zip was too long and needed cutting down.)
Next you need to pin or glue your zip to the back of your opening. Pinning will more likely shift it out of the way so I like to use a specific sewing glue such as the Hemline glue pen.
I always go overboard on my glue but it dries clear and doesn't gunk up your needle so the more the better in my mind!
So now turn your fabric right side over and position your zip in the opening.
Change your presser foot for your zipper foot (or piping foot) to sew this and sew very slowly.
This is an adjustable piping foot. BUY ONE NOW, it will change your life.
These types of zips do take practise but if you're slow and steady you can achieve a professional finish easily.
Sew along the edge of your fabric opening trying to keep your zip straight. As you approach the zip pull leave the needle down and lift the presser foot.
See how close you can get with this foot?
Unzip the zip until the pull is out of your way, lower your presser foot and sew on until you need to re-zip.
Continue round all 4 sides of your opening.
Ignore the blue glue, it dries and disappears in a couple of hours. See how neat and close my stitching is the with piping foot? That's not from practice, it was like that the first time I tried using it as opposed to my zipper foot!
Pin the second pocket piece to the front pocket piece on the back of the lining without catching the lining piece and sew around all four sides.
That's your zipped pocket done. :)