Quick groundcovers from seed for newly excavated area

Just did some earthworks & no unfortunately I didn't plan ahead.  I want it to be a dappled shady garden area, where there's already a Amelanchier canadensis (Serviceberry), and I'll be planting a few citrus, a crampbark, maybe a white mulberry which will be heavily pruned or coppiced every once in awhile if more sun is needed.   Currently while the bushes/trees are young the area gets full sun, at least in summer, perhaps in winter the nearby shed might throw some shade in the afternoon.  
Just looking for suggestions for quickly germinating & growing groundcovers?  Currently it's the middle of summer but presumably they'll only be up to a month more of dry warm weather before autumn rains and a bit of a drop in temperatures.  
Preference is for edible/medicinal or otherwise useful plants but anything that provides cover & colour and is not easy to remove down the track when I'm planting more would be great.  

I'll put down Some bought topsoil and/or compost (though it's not scraped down to nothing, there is some variation in the amount of topsoil left over the site) I think and heavily mulch most of it as well, maybe lightly with woodchip & somewhat heavy with hay as that's what I have freely available (I know, I'll be weeding out grass etc because of that, unfortunate, but my veg garden has still certainly done a hell of a lot better with the hay thickly mulched over it than the 2 years previously when I didn't mulch) I guess leaving some spots open where I'll scatter the seeds...

if summer will be over in a month, you might consider winter rye.

Winter rye is an excellent ground cover for cooler months as it dies back when warmer weather comes along.

Oats is another possibility. Around here road crews use oats in ditches and berms for quick stabilization of the soil while slower germinating permanent plants are getting started. Advantages are it sprouts fast and is vigorous, but short season so in just a few months you can put something else there.

I do like the idea of oats, I could maybe get a milky oat harvest out of it as well.  I wasn't really thinking about a cover crop as such but makes sense to sow something like that as well as other more long term groundcovers...