Quick prep? (rub or marinade?) for Flat-Iron cut?

[RPMcMurphy]

The NJ weather has me wanting to throw something on the grill this evening. I'm planning on picking up a couple of flat-irons and firing up the weber.

I'm a rather novice cook, and unfortunately don't have more than say, 30 minutes to marinade. Are there any rubs I can whip together that will still give some flavor without a long marinade time?

I'm a little pressed for time as I have an engagement later tonight, but can spare 30minutes an hour while I whip up some veggies. I plan on a little horseradish mustard on top.