Use your zig-zag stitch and appropriate foot. Set your stitch length to zero
and width can be as wide as you want. Make a few stitches then move
your quilt layer to the next spot you want to tack, etc. Like most quilting,
start in the middle and work your way out. Probably easier to mark the
spots at regular intervals before tacking.
Don't know which sewing machine you have but some machines have
a special stitch for tacking. I have one on my Janome 6600 that looks
like a big asterisk.