If you're trying to get neuromuscularly efficient at 5k pace, doing something like 16-20 x 400m @ 5k pace w/ 60s (or 100m walk/jog) recovery might be your best bet. 10-12 x 400m @ 3k pace would also do the trick. Those are the sort of workouts that make running 5k pace feel easy (or easier, anyway).
If you're trying to do a bread and butter workout to improve overall fitness in a way that specifically targets 5k racing, 6 x 1000m @ 5k pace w/ 2:30-3 minutes (or 400m walk/jog), 8 x 800m, and 5 x 1200m with similar recovery ratios (just less than the time of the interval) will also also do the trick.
Doing one of these workouts a week for a month (say, 16 x 400m @ 5k, then 6 x 1000m @ 5k, then 5 x 1200m @ 5k, then 12 x 400m @ 3k) in addition to your current CV work would be great preparation for a peak 5k.