Throw your plywood onto your router table and get to work!
I assume you know how to operate it.
I used a 1/4" upcut end mill. This has left a messy cut that will require some sanding to clean up.
I also thought that I could pick up .25" spline at the local hardware store (turns out I can't) so I routed 1/4" grooves into the frames as well. If you have a tool that will cut appropriately sized grooves this would be a good time to do it, otherwise, skip that step and just cut out the frames.