I wanted to use screws, because I like a tight fit, with this design, I got exactly that.
Step 1: What You'll Need
2 flat LEGOs 2x3
1 flat LEGO 2x12
1 flat LEGO 2x8 (with holes in it)
Step 2: Assembly
Put to two 2x3's on the back of the 2x12, one in each side. They will work as spacers, leaving enough room for the screws.
Put your favorite minifigures on front (or whatever you can spare)
Put to two screws through two holes in the 2x8, and place the 2x12 assembly on top.
And that's it.
(You'll need to take off the 2x8 again, before putting it up on the wall)