Using 11/16" stock wood from a local hardware store, I started with two 36" vertical strips. 18" at a time, however, may look better if you have few medals.
I then spaced out the 12" horizontal strips in a way that would accommodate different medal sizes.
I spaced these out at 2" and 4" in the pattern you see in the photos. I predrilled and set in countersinks to use #6 X 1" drywall screws, although 1.25" might work better. I glued the connecting spots and set the screws in from the back.
The medals are most easily placed from bottom to top and I used a staplegun with 5/8" brads on the ribbons.
For a from-the-hip project, I'm very happy with it!